I had problems with users with dots in there usernames as we use the same username as there college ID's and I git around it by altering the RewriteRules. Here's what I have now and for the life of me I can't remember which one I altered & I can't find my original download :-)

RewriteRule ^admin$ - [L]
RewriteRule ^admin/(.*) - [L]
RewriteRule ^install$ - [L]
RewriteRule ^install/(.*) - [L]
RewriteRule ^$ index.php
RewriteRule ^view/(.*)/(.*)/ view_video.php?id=$1 [L,QSA]
RewriteRule ^tag/(.*)/(.*) tag.php?search_id=$1&page=$2 [L,QSA]
RewriteRule ^channel/(.*)/(.*)/recent/(.*) video.php?category=recent&chid=$1&page=$3
RewriteRule ^channel/(.*)/(.*)/viewed/(.*) video.php?category=viewed&chid=$1&page=$3
RewriteRule ^channel/(.*)/(.*)/ channel_detail.php?id=$1

RewriteRule ^detailed/recent/(.*) video.php?category=recent&page=$1&viewtype=detaile d
RewriteRule ^detailed/viewed/(.*) video.php?category=viewed&page=$1&viewtype=detaile d
RewriteRule ^detailed/discussed/(.*) video.php?category=discussed&page=$1&viewtype=deta iled
RewriteRule ^detailed/favorites/(.*) video.php?category=favorites&page=$1&viewtype=deta iled
RewriteRule ^detailed/rated/(.*) video.php?category=rated&page=$1&viewtype=detailed
RewriteRule ^detailed/featured/(.*) video.php?category=featured&page=$1&viewtype=detai led
RewriteRule ^detailed/random/(.*) video.php?category=random&page=$1&viewtype=detaile d
RewriteRule ^recent/(.*) video.php?category=recent&page=$1
RewriteRule ^viewed/(.*) video.php?category=viewed&page=$1
RewriteRule ^discussed/(.*) video.php?category=discussed&page=$1
RewriteRule ^favorites/(.*) video.php?category=favorites&page=$1
RewriteRule ^rated/(.*) video.php?category=rated&page=$1
RewriteRule ^featured/(.*) video.php?category=featured&page=$1
RewriteRule ^random/(.*) video.php?category=random&page=$1
RewriteRule ^rss/new/ rss.php?type=new [L]
RewriteRule ^rss/comments/ rss.php?type=comments [L]
RewriteRule ^rss/views/ rss.php?type=views [L]
RewriteRule ^group/(.*)/members/(.*) group_members.php?urlkey=$1&page=$2
RewriteRule ^group/(.*)/videos/(.*) group_videos.php?urlkey=$1&page=$2
RewriteRule ^group/(.*)/add/(.*) add_video.php?urlkey=$1&page=$2
RewriteRule ^group/(.*)/fav/(.*) add_favour.php?urlkey=$1&page=$2
RewriteRule ^group/(.*)/topic/(.*) group_posts.php?urlkey=$1&tid=$2
RewriteRule ^group/(.*)/invite/ invite_members.php?urlkey=$1 [L,QSA]
RewriteRule ^group/(.*)/ groups_home.php?urlkey=$1 [L,QSA]
RewriteRule ^groups/(.*)/(.*)/(.*) groups.php?chid=$1&page=$3
RewriteRule ^groups/(.*)/(.*) groups.php?category=$1&page=$2
RewriteRule ^include/(.*) http://www.vshare.in
RewriteRule ^pages/(.*).html$ show_page.php?name=$1 [QSA,L]
RewriteRule ^([^/]+)/favorites/(.*) user_favorites.php?username=$1&page=$2
RewriteRule ^([^/]+)/playlist/(.*) playlist.php?username=$1&page=$2
RewriteRule ^([^/]+)/friends/(.*) user_friends.php?username=$1&page=$2
RewriteRule ^([^/]+)/public/(.*)$ user_videos.php?username=$1&type=public&page=$2
RewriteRule ^([^/]+)/private/(.*)$ user_videos.php?username=$1&type=private&page=$2 [L,QSA]
RewriteRule ^([^/]+)/groups/(.*)$ user_groups.php?username=$1&page=$2 [L,QSA]
RewriteRule ^([^/\.]+)?/?$ user.php?username=$1 [L,QSA]