OK my error I was mistaken in my post refering to it as a laptop.
Yet still when I pull up your E600 on HP's site Drivers & Support Docs, and click on the all operating systems it only shows XP drivers. Acer Support - Drivers & Support Documents
Which could be installed in compatibility mode XP Compatibility Mode
If you have a link where it shows Vista drivers for your E600 with Realtek Vista drivers then you can use them in compatibility mode as well just select Vista.
If you know the Realtek model number you can also get them from here.Latest Realtek HD Audio Driver Version
Or try Windows update