hello newbie question here, sorry coz dli jud ko techy when it comes to pc hardware stuffs, pls bear with me

this is my mobo: asus p5kpl-am epu
ASUS - Motherboards- ASUS P5KPL-AM EPU
this is my current vcard: geforce 8500 gt - yes, a bit ancient

psu: (generic) tommade 600watts from interpace
im planning to upgrade my vcard, to maybe knang HD 5670
ATI Radeon , this is the only price range na ako ma afford, i saw one selling in the b/s section, still deciding if i will opt to buy a bnew or a 2nd hand. perhaps naa sad mo ma suggest na mas better at same price range ? and reason na mu upgrade ko is knang I want to play skyrim on my pc, ok ra man cguro akong cpu (core2duo) and 4gig ram.
my 1st question: naa ba issue sa compatibility ? coz reading through some of the specs, the vcard has a "PCI Express 2.1 x16 bus interface", while my mobo only have the following slots: 1 x PCIe x16, 1 x PCIe x1, 2 x PCI. mowork ba cya as backward compatibility ? does it have any drawbacks ?
my 2nd question: some pics i saw sa mga videocard karon kay naa lageh cya power cable/connection/wire from the psu, para sa unsa dae na cya ? coz on my 8500 gt, dretso ra man cya paslak sa pcie slot and no other wirings needed. again dli jud ko familiar kau sa mga hardware stuff, and if ever sa 5670 na vcard (posted above) needed ba na cya anang xtra cable ?
thx much