You cannot run Vista on a PS3. In order to do that, you need to emulate an x86 based processor on a powerPC, and emulation right now gives you about a 200MHZ PC, which is way under the reqs for Vista. Plus Sony locks out the 3D, so no Aero until the PS3 is hacked. Windows 98 and XP are possible though incredibly slow, and threads exist in the PS3 linux forums.
PS3 on PC is even more improbable. You need approximately 10x the power to emulate a system. Even if it was 1:1, you would still need a machine as powerful as the PS3 meaning 8 cores, advanced gfx, etc. which just isn't feasible now, or for many (10+ years). To put this into perspective, a 3.2GHZ Dual Core with GeForce8800GTX can barely emulate a PS2.