Grandma's Pavillion P-3_max hard drive size & type

Hi, not sure which forum to post this.

Someone gave my elderly neighbor a Pavillion 6465 P-3 desktop w/o a hard drive.
Told her I'd try to find what kind & how much for replacement.

It's got Celeron 433 MHz.

Found very few HDD tech specs searching HP's site, but found on Drive Solutions the exact model: http://www.drivesolutions.com/cgi-bin/shop/ugdtstore.cg...
says the orig HDD was 9.6 GB EIDE 5400 rpm. Says the model has 2 IDE connectors.

Question 1: what is max size HDD this pc is likely to support?
The upgrade HDDs Drive Solutions shows are mostly ATA100, either 5400 / 7200 rpm (same link as above).

2) Given HDD size limitations of the pc, what is likely cheapest size / type commonly available for it now? Will just a "standard" ATA 100 (of what ever size) work?

3) Would an EIDE Ultra ATA 100/133 work, within size limitations?

Thanks.