upgrading

Guys,

I'm wondering if anyone can offer any help or advice, or even point me somewhere to get the answered to these questions.

My site is currently using drupal 4.7.3 (yes i know i'm bad for not upgrading) and I would like to upgrade it to make it secure.

I have the following modules being used

actions
authorship
captcha
chatbox
contact_list
event
formsingle
image
img_assist
inline
links
linksdb
notify
smileys
ststiatics_filter
urlfilter
workflow

Ideally I'd like to move to 5.1 however I understand that not all modules will work on that. I also am using pgsql instead of mysql can someone with more of a clue please advise what would be my best method of upgrading the site and how long it should take.

NOTE: some of the modules needed to be edited due to the fact they didn't work with postgres.

Thanks for any help

Cath