I think you'd have to buy a new key to use your account on a PC. Upgrading a PS3 standard edition to PS3 CE won't let you play on the PC. Though, i'm not sure if buying a Windows CE on steam (or i think gamestop if it's still on sale) and adding it to your account will flag your account for Windows, as well as the CE goodies since it would be account wide.

Probably best to dig a bit more on this before purchasing either or.