Because of your space and noise restrictions and budget, onboard would most likely be fine. Personally, I would suggest you go for the Guillemot Fortissimo 7.1. Economical, and all told a good card.
As for speakers, I don't have any experience because my computer is hooked up to my home theatre, not some cheesy computer speakers ;-)
XP 2500+ Barton @ 2241Mhz
2x512MB Corsair PC3200
MSI GF3Ti 500
2x80GB 7200RPM Maxtor