This is a very broad question, it all depends on what you're going to do. Are you working in DV25 exclusively? If you're going DV on the PC I would recommend Sony Vegas with a firewire card and a digital to analog converter box for your analog needs. If you're wanting to do broadcast quality stuff I would definitely recommend one of the flavors of VelocityQ (there's a 5k, 7-8k and 10+K priced versions, that's software / hardware bundles. If you go turnkey those prices will increase). There's literature on both websites to get the details on what each can do, if you give me a better idea on what you'll be doing I can give you a better idea on which system might be better for you.
- mYthprod
(John David Hutton)
* Build Your Own VelocityQ. See how * :
http://www.customflix.com/Store/ShowTtl.jsp?id=205835