I just checked out my comp it does use pci-e video card so i can slap this right in there right?
http://www.newegg.com/Product/NewProduct.aspx?Item=N82E16814150439&cm_re=gts_250-_-14-150-439-_-Product
Ive dealt with several of these HP cases and you will defiantly have issues fitting that card in it. I would for sure measure the clearance you have in the case to allow for the card.
Also the power supply you have is a 350 W
I have removed the guts from several of these HP computers and installed them in newer larger cases with no problems at all
Personally I would recommend, if finances allow it to get a case/PSU combo . You will benefit for power needs. future upgradability and case cooling.
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01498952&tmp_track_link=ot_faqs/top_issues/en_us/c01498952/loc:2&lc=en&dlc=en&cc=us&lang=en&product=3774377