Almost all systems have audio built in to the mainboard, no sound card needed. Most people buying sound cards now are doing it for 7.1 sound.
4MB RAM is fine.
The current line of Intel budget processors is the Core i3 line. Don't be satisfied with anything lower than the Core CPUs. AMD has not really kept pace with Intel in recent years.
Many modern systems are delivering with Win8. You may get a better custom system from a builder such as
Directron. (click on PCs & Barebones, System Specials. Sort by price. Add $100 to the price because the OS is not automatically included.) Although you could build one yourself or get me or Jim to do it for you.
Newegg sells major PC company systems, but only recently. They are more of a parts company.
The oh wow component these days is the solid state drive. It's expensive. It's worth it.
If you need a monitor, there's nothing wrong with getting a 23" Acer from Newegg for about $120, or the 24" for $140.