Yes, good luck with it all - let us know how you get on!
How long 'til you finish?
By the way, with the no-sound thing, I think I might know what's gone wrong
It's very similar to a problem that I have
New graphics cards with HDMI outputs etc. tend to have a built-in sound card (so you can output your audio on your TV with HDMI cables and not have to use *another* cable for the sound). When windows installed the drivers for your graphics card, it would also install drivers for the sound card.
When Windows installs a new sound card it sets that as the default sound output, so when you installed your shiny new graphics card it would have set the built-in audio chip of that to output sound by default. Go to your sound control panel and you should be able to change your default audio device from the new one built into the graphics card (normally comes up as 'Hi-Definition Sound Device' or something similar) to your sound card.
I have a similar problem - got my ATi Radeon HD 3870 (so 2x Hi-Definition audio devices for that, one for each of the two HDMI outputs), plus on-board sound on the motherboard (use it for the coaxial S/PDIF out), AND the SoundBlaster X-Fi Extreme Audio (use it for the optical S/PDIF out to my Hi-Fi).
If you're in Windows 7 right-click the volume control in your task bar and select 'Playback Devices'. It brings up a list of all your audio outputs currently enabled. Right click on the one it should be (your sound card I'm assuming) and pick 'Set as Default Device'. Identical process for Windows Vista. It will be slightly similar for Windows XP, but I don't have that installed any more to check the exact names and menu options to pick.
Of course I've assumed your new graphics card is one of the more recent hi-definition capable ones which has a built in sound card.
HTH