Using XFX HD4850 in HTPC

I will be purchasing a XFX HD 4850(this one http://www.newegg.com/Product/Prod [...] 14150337).
My main concern is that whether it will fit my antec NSK 2480 cabinet.I will have to remove my tv tuner card to accommodate it as it uses 2 slots.
I am having an antec EA 430 W PSU whereas the recommended PSU is 450 W.
I have the following config
Panasonic 37" HD Display
HTPC - Antec NSK 2480 HTPC Case
Intel Core 2 Duo E7300 @ 2.66 Ghz
Asus P5KPL-CM
G-SKILL 4GB 800 MHZ Dual Channel
Sony DVD RW SATA
Western Digital 500 GB Green
Windows Vista Ultimate 64 Bit

My motherboard has a pci 1.0 slot .The 4850 is a 2.0 card . Will the card run at half its strength. Some say only gtx 260 card and above actually use the entire bandwidth of a 2.0 cards the rest don't even use the entire bandwidth of 1.0 slot hence it wouldn't really make a difference. Is it true?

I was earlier using a xfx 9800gt but for some strange reason the screen would go blank for a few seconds and come back up(there would be no bsod,freeze).I have returned this card in lieu of the above one.

Was the PSU to blame in the above case or just that nvidia drivers are buggy.

I will be running the 4580 card @ 1360x768 60hz mostly for watching HD movies I hope it runs crysis, and the latest games of 2009 at full settings.