Drop Zone will; don't have PSYN II, but it most likely will if it came with LE.
Cakewalk used to have a few free (older) synths, but it looks like Square 1 is the only one offered now.
Search 'free vst soft synths' on the web and take a chance. Most will work and some will be worth the effort. Some will not and there's always a chance of catching something bad.
I see you have Vista. See if Proteus VX is still available for free. A good synth with over 1,200 patches.
And DSK. I've downloaded some of their stuff; some worked.
But the best synths will be the ones you pay for and they come with support and upgrades and patches (usually).
http://www.store.cakewalk.com/b2cus/category.aspx?categoryid=47&startpage=2 Square 1
http://www.dskmusic.com/category/synths/