Q: Please provide some informative answers, not Yeses or Nos. Thanks
A: yes it is. the card requires a 16x pci-e slot, which your machine has. http://reviews.cnet.com/desktops/hp-pavilion-media-center/4507-3118_7-31956770.html HOWEVER, the 9800gt is just a rebadged 8800gt. There is NO difference in performance between the two cards. I dont know what you are paying for the 9800gt but an 8800gt can be bought on tigerdirect.com for $110. If you are considering a gtx or a gtx+ the radeon 4850 is a better buy. Faster than the gtx and a lot cheaper. The only other factor you need to consider is the size of the power supply. I think the a1540n only has a 300 watt psu. if thats the case, you will need to upgrade this to a 450 rated. These retail for about $50.