If starting out, buy a refurbished or second hand mac, it really is a lot more straightforward for doing this type of stuff. If you can get one of the intel imacs they are extremely powerful for the cash and allow you to run programs like finalcutpro and shake which you won't find on other platforms.

If going the PC route and cash is the main concern, pick up a cheap PC and install ubuntu linux and download cinelerra http://heroinewarrior.com/cinelerra.php3
it can do almost everything the big expensive programs can and is completely free as is ubuntu.

So your only cost then is the hardware itself.

Otherwise you can go Windows and check out doom9.org and the guide mentioned above.