You really should read the links you post, ovaltine. The HP a730n HAS A PCI-E SLOT. Overall, if you know how, schuyler, get a new case plus PSU (If you haven't already), and just move the system to a bigger case. Also, if you haven't already, upgrade the RAM as well.
thanks for the help, I know in a perfect world I would get a better computer but I have limited funds, I have gotten 4g of RAM and a pentium 4 3.8ghz but I just want to upgrade the video card better than my ati radeon x700 PRO so I can get the best out of the motherboard that I can, I just need a video card that's at max 9.5 inches long since I found out the hard way by buying a ati radeon x1950 xtx just to find out it didn't fit on the motherboard since it stuck out over the power cord to the mothboard and I've now had to send it back for a refund and for some reason video card companies don't make the length of their video cards very evident even though you'd think that would be worth making very evident.
Are you sure the X1950XTX is over 9 inches long? How long inside the case? 9 inches right? + add the PCI-e power cable.
Most 8800GT, 8800GS, 9600GT cards are 9 inches inside the case. Some are 8.5 inches. There may be some just a bit over 8 inches. Those are cheap (in USA anyway) and upgrades from a X1950XTX. But most of the cards under 8 inches will be slower than the X1950XTX.