Integration with phpbb - clean urls/htaccess confict

I've got an existing static html site which I've converted to drupal. This site had an existing phpbb forum which has an SEO URL mod. It seems like the drupal clean urls htaccess is conflicting with the phpbb htaccess causing the phpbb links to not work. Currently they just go to the site's home page, or a page not found error, with the forum url in the address bar.

The existing phpbb htaccess is:

RewriteRule !\.html$ - [L]
RewriteRule ^forum/[a-z0-9-]+-([pt])([0-9]+)\.html$ /forum/viewtopic.php?$1=$2 [L]
RewriteRule ^forum/[a-z0-9-]+-f([0-9]+)\.html$ /forum/viewforum.php?f=$1 [L]
RewriteRule ^forum/[a-z0-9-]+-c([0-9]+)\.html$ /forum/index.php?c=$1 [L]
RewriteRule ^forum/[a-z0-9-]+-u([0-9]+)\.html$ /forum/profile.php?mode=viewprofile&u=$1 [L]
RewriteRule ^forum/([a-zA-Z0-9_]+),([^/,]+),([^/,]*)([^/]*\.html)$ forum/$1$4?$2=$3 [QSA,N]
RewriteRule ^forum/[a-z0-9-]+-([pt])([0-9]+),([^/,]+),([^/,]*)([^/]*\.html)$ forum/viewtopic\$5?$1=$2&$3=$4 [QSA,N]
RewriteRule ^forum/[a-z0-9-]+-f([0-9]+),([^/,]+),([^/,]*)([^/]*\.html)$ forum/viewforum$4?f=\$1&$2=$3 [QSA,N]
RewriteRule ^forum/([a-zA-Z0-9_]+)\.html$ /forum/$1.php [L]

If I comment out the drupal rewrite rules the phpbb rules work fine, but then drupal's don't. Has anyone experienced this in the past?

I'm familiar with some htaccess but I'm afraid this is way over my head. Any help would be greatly appreciated!

Thanks!