BBcode doesn't seem to be converting....& miscellaneous other

First: the BBcode is just displaying all the tags

This is almost certainly a problem with your input filters. Although, IIRC, there is some vBulletin-style BBCode that doesn't work with the Drupal BBCode module, but this is a minority. If none of your BBCode is working, it's more likely the input filters aren't set up correctly. :)

Problem two: extremely slow response when I click topic links.

Probably need to get MySQL to rebuild it's tables and indexes. Generally, threads (depending on the speed of the hosting, and how many/what modules are installed) should load quickly. I run this on the server's command line when MySQL is going slowly:

mysqlcheck -u<insert username here> -cep --auto-repair <insert drupal database name here>
mysqlcheck -u<insert username here> -op --auto-repair <insert drupal database name here>

If this doesn't help, you may need to look at optimising your MySQL installation, getting a faster host, installing an opcode cache, or removing some Drupal modules.

Now let's look at the errors:

user warning: Unknown column 'skype' in 'field list' query: INSERT IGNORE INTO sharpe5_sid512.profile_values (fid, uid, value) SELECT fid,
userid+1000000, skype FROM user, sharpe5_sid512.profile_fields WHERE name="user_skype" AND skype<>""; in /home/sharpe5/public_html
/000/includes/database.mysqli.inc on line 156.

Not important, there was no Skype column in the vBulletin user table.

user warning: Unknown column 'attachment.extension' in 'on clause' query: INSERT IGNORE INTO sharpe5_sid512.files (fid, nid, filename,
filepath, filemime, filesize) SELECT attachmentid+1000000, threadid+1000000, CONCAT((attachmentid+1000000), '_', filename),
CONCAT('files/', (attachmentid+1000000), '_', filename), TRIM(LEFT(MID(mimetype, LOCATE('Content-type:', mimetype)+LENGTH('Content-
type:'), LENGTH(mimetype)), LOCATE('"',MID(mimetype, LOCATE('Content-type:', mimetype)+LENGTH('Content-type:'),
LENGTH(mimetype)))-1)), filesize FROM attachment INNER JOIN thread ON attachment.postid=thread.firstpostid INNER JOIN
attachmenttype ON attachment.extension=attachmenttype.extension; in /home/sharpe5/public_html/000/includes/database.mysqli.inc on
line 156.

user warning: Unknown column 'attachment.extension' in 'on clause' query: INSERT IGNORE INTO sharpe5_sid512.comment_upload_files
(fid, nid, cid, filename, filepath, filemime, filesize, description, list) SELECT attachmentid+1000000, threadid+1000000,
post.postid+1000000, CONCAT((attachmentid+1000000), '_', filename), CONCAT('files/', (attachmentid+1000000), '_', filename),
TRIM(LEFT(MID(mimetype, LOCATE('Content-type:', mimetype)+LENGTH('Content-type:'), LENGTH(mimetype)), LOCATE('"',MID(mimetype,
LOCATE('Content-type:', mimetype)+LENGTH('Content-type:'), LENGTH(mimetype)))-1)), filesize, filename, attachment.visible FROM
attachment INNER JOIN post ON attachment.postid=post.postid INNER JOIN attachmenttype ON
attachment.extension=attachmenttype.extension; in /home/sharpe5/public_html/000/includes/database.mysqli.inc on line 156.

user warning: Unknown column 'filedata' in 'field list' query: SELECT attachmentid+1000000 AS uniqueid, filename, filedata, 0 AS avatar
FROM attachment UNION SELECT IF(userid=0,0,userid+1000000) AS uniqueid, filename, filedata, 1 AS avatar FROM customavatar; in
/home/sharpe5/public_html/000/includes/database.mysqli.inc on line 156.

Do you have post attachments stored in the database or on disk? My suspicion is these errors have been caused by file attachments being stored on disk instead of in the vBulletin database, I might be wrong though.

You may need to copy over file attachments manually.

user warning: Unknown column 'folder_fid' in 'field list' query: SELECT MAX(folder_fid)+1 FROM privatemsg_folder in /home/sharpe5
/public_html/000/includes/database.mysqli.inc on line 156.

This is more worrying, vbtodrupal couldn't find a folder list for private messages. Check your PMs have been copied over correctly.

These errors are very unusual: are you running a very new, or very old copy of vBulletin? What version -- of vBulletin, exactly -- are you running this import on?

I'm getting off the thread topic here but, what does vbtodrupal do if it encounters user accounts that already exist?

For the most part, vbtodrupal just sends SQL to MySQL, so it doesn't even know if there are duplicate accounts. However it does add 1,000,000 to all ids in the database, including uids, to avoid conflicts. The problem with users is that the name and mail columns must be unique. For example, if this data is already in the Drupal users table:

+-----+-----------------+-----------------------------------+
| uid | name            | mail                              |
+-----+-----------------+-----------------------------------+
|   1 | Mr Test One     | test-one@example.com              | 
|   2 | Mr Test Two     | test-two@example.com              | 
|   3 | Mr Test Three   | test-three@example.com            | 
|   4 | Mr Test Four    | test-four@example.com             | 
+-----+-----------------+-----------------------------------+

Then we try to import this from vBulletin:

+---------+-----------------+-----------------------------------+
| uid     | name            | mail                              |
+---------+-----------------+-----------------------------------+
| 1000000 | Mr Test One     | test-one@example.com              | 
+---------+-----------------+-----------------------------------+

The import of Mr Test One will fail. Furthermore, any topics/posts written by Mr Test One will be imported, but with the uid set to 1000000; as the import of that user failed, Drupal will not be able to attach the post to a user and the post will 'disappear'.

Note: your mileage on the above information may vary, it's based on my own limited experience, which I don't have time to test!

I believe what I can do is just rename the existing accts before I import vB.

Sounds like a good idea. You could use a SQL query like this to update all the Drupal users:

UPDATE users SET name = CONCAT('prefix_', name);

And for the e-mail address:

UPDATE users SET name = CONCAT('prefix_', mail);