First - if you want to use it free, yes you need CygWin. There are commercial ports of Postgresql (or postgresql-based databases) to Windows. It's not that hard to get working under Win, if you use the cygwin postgresql install... Assuming you get the cygipc stuff working ok (I think it might need an earlier version than 2.xxxx or was it 1.2.xxx (unsure) cos I tried it with the default ipc-daemon and no luck (IPC errors). We got it running as a service using instructions on techdocs.postgresql.org (Win FAQ or linked off it or something). I think cygwin current version may not select all required packages to get it working, you may need perl and some stuff that will auto-select to get it on; I remember reading somewhere...
ODBC works fine, have had remote connections to it (on Win2k) with no problem. Apparently WinXP may (or may not) have some issues running it under CygWin.
See pgAdminIII for admin, both remote and local.
If you're connecting locally, you may (again, unsure) have to use the cygwin libraries; but from any further away it's exactly the same interface. Dunno if secure ssh connections to it work though (not tried it).
As the site says, it's not proven for production sites but I haven't found any problems yet. Running it under Linux really isn't hard though when you do want to make a known-stable platform for production/whatever.
It doesn't look like people see this forum that much from my few posts that I've made, but hope I've been of help.