You didn't need to post the specs, all we needed to know is that you have an HP Pavilion p6213w.
It's not absolutely necessary that your system has a PCIe x16 2.0 slot in order to use a 2.0 card. According to PCI-SIG, cards and motherboards that use the PCI Express interface are forward and backward compatible between the 1.x spec and the 2.x spec.
The GTX 460 will work in that system as long as you upgrade your power supply, your systems stock 250W psu (power supply unit) won't cut it.
Your systems specs-
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01869190&tmp_track_link=ot_faqs/top_issues/en_us/c01869190/loc:3&lc=en&dlc=en&cc=us&lang=en&product=4006023#N349According to nvidia, in order to use the GTX 460 your system will need AT LEAST a 450W psu with two 6 pin pcie power connectors. (see Specifications tab)
http://www.nvidia.com/object/product-geforce-gtx-460-us.html Most 450W psu's will only have one 6 pin connector, but most 500W or greater psu's will have at least two. That system uses an ATX power supply, very common and easy to replace. I'd recommend Antec, Corsair, Enermax, OCZ, Seasonic or Silverstone, all are decent brands.
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007657%20600014006&IsNodeId=1&bop=And&Order=RATING&PageSize=50If you're in Canada-
http://www.newegg.ca/Store/SubCategory.aspx?SubCategory=58&name=Power-Supplies&Order=RATINGJust make sure that the power supply you get has all of the connectors that you'll need.
For example:
Your systems motherboard uses a 4 pin 12v ATX connector for the processor (a 4+4 pin or 8 pin will also work, you only use what you need) and a 24 pin main.
Graphics card needs 2x 6 pin pcie power connectors.
And whatever SATA or Molex connectors that you need for the drives (HDD and DVD).
Motherboard specs-
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01324212&lc=en&dlc=en&cc=us&product=4006023