This get's asked a lot, but what we really need is more info. I'll give you the basics that may get you going though.
You will want Perian QuickTime Codecs (free). Install these, and it will help your mac play a lot more files. If you've already done this, then what filetypes aren't playing in Front Row? (wmv, avi, flv)
A good converter is Visual Hub, about $20 or 30, but well worth the money if you have 200 Gig of Video. You can use that to covert everything to .mp4 with h.264 encoding. It will take a while, so I suggest doingn about 8 at a time, and giving it several hours to complete. The h.264 encoding takes quite a while. If you just to straight mp4 then it's much shorter.
If you don't want to spend that money, then you can use VLC to do the conversion, go to the os x techtips link in my signature, and I have instructions on how to do it, but it's one video at a time. Just replace the .bin with whatever filytype you are converting.
Best,
Brian
Is there a way to convert all my videos (some 200 gig) so they'll play in Front Row?
There's a lot that won't, so I use VLC to play them. I'd rather I could just use Front Row to play them so I can sit on my arse and use the remote!
How do I do that?