P4P800 - Upgrades

Enjoying my new P4P800-SE and am thinking about a few other upgrades.
Appreciate any opinions:

1) Current video card = ATI radeon 7000 agp4x - primary use is 2d - any
advantage (2d speed or clarity) in upgrading to a radeon 9xxx series?

2) Using a Seagate 80gig ATA100 7200rpm drive ; would a SATA drive be
noticeably faster? Can a SATA drive (fat32) be booted to DOS (if needed
for file access) & also be used with format and fdisk (like a standard ide
drive)?

2) Lastly, using onboard sound (AD1985) - not bad quality ; would a basic
SB PCI card sound much better for playing music?

Thanks.