I'd imagine that right now vmware is probably the fastest way to run it, but running it through cygwin is more tested. cygwin is not gonna win a gold medal for how fast you can fork processes, so a server that builds and tears down a lot of connections is gonna be pretty slow running postgresql.
Now, you could reverse thvmware / linux thing, and put linux / vmware underneath with postgresql, then load win2k server on top in vmware and run your web server / app server software there. That gives you the added advantage of having a very stable windows server due to vmwares ability to make the "box" that windows is running on appear to be ultra stable.
Again, if it's a low load site, then postgresql under cygwin is probabl the easier, closest to click and point install out there. Postgresql is an option when installing cygwin, so you just select it and go.
