1. How good is the software that comes with your tv tuner?
2. How cheaply could you get a copy of Ultimate?
I like using Vista Media Center for my TV and DVR needs. It works well and does what I want it to. It is a lot better than the software that came with my Hauppauge tuner, and because I got it free from college (even after graduating, somehow), it was a no brainer. I would think a lot of schools have campus agreements with MS where you could get a free license for certain OSes. Also, there are some free DVR software suites out there (MythTV, I think?). If you can't get Ultimate for free, I would check out some other options first to see if they suit your needs.
Alternatively, you could download Windows 7 beta which comes with media center that has (in my experience) improved tv tuner functionality. It's free and will work until at least August. Maybe Vista will be free by then, who knows?