Hi Fran,
unless you have a creative soundcard you can't use Vienna. I can use it because I have a usb Audigy nx2 soundcard for my laptop as well as the software setup to run soundfonts (Forte, midiyoke etc etc)

Soundfaction alive does a great job if you want to build up a font of your own, or just replace the odd sound. You can just mix n match to your hearts content.
Bear in mind, bigger is not neccesarily better. The commercially sold ones don't always sound better than the freebies either.
I was auditioning about 8 different piano's from various gm fonts the other day for one of the biab midifiles. Surprisingly to my ears, the 2 that sounded the best was the 30+ mb piano from sgm180 and a 1 mb piano from one of the other freebie fonts. The ones from my commercial gm fonts , sounded lousy with that particular tune.
Beauty of the soundfont system is, I could create a font that can incorporate all 8 piano's into various banks or just ditch the ones I don't like.

I'm even considering recording my sd1 drums as a font.

The font system may be a bit old hat, but it sure is versatile.

AJ, I came across rather an interesting font the other day on ebay. One of your posts you mentioned something about Korg. Must admit at times I miss the amazing sounds of the Wavestation. You mentioned you had it and others in some sort of a softsynth?? I remember looking it up, but the price here, floored me.
Anyway I found a 650mb soundfont full of pads, bells, spooky etheral sounds etc. Wavestation it's not , but it's interesting.
I have to break it up as my current laptop can't play a 650mb font. For $24 and 8 hours of download time, I figure I didn't have anything to lose.
He's done some early model synths as well.

best wishes
Rikki