Postgresql installation is what matters, installations of PT3 and 4 are of no use in recovery alone (you can just reinstall those from the internet). Hopefully your postgresql installation folder is intact.
on the new hard disk you must have installed the identical major.minor postgresql version as you were using on the old hard disk. eg. 8.4.12 it is fine to install/use the latest 8.4.x, but not 9.x.x. Hopefully that's clear.
Once you have the correct postgresql version installed (you can tell by it's folder name in \program files)
use services.msc and stop the postgresql service.
copy the \data subfolder from the old one, directly over the \data folder in the new.
use services.msc and start the postgresql service.
it should now have all your old databases present