We also have a Dimension 3000 and it's served us well. In fact, I just reloaded the OS so my daughter can squeeze another year out of it before she heads to college next fall.

The current model line that replaced Dimension is the Inspiron desktop. The current basic home model is the Inspiron 546. One advantage of getting a new desktop now is you'll be able to upgrade to Windows 7 for free. Alternatively, you might think about waiting until October to order one, since they will then come with Windows 7 installed.

Here the link to this model is you can to take a look:
http://www.dell.com/us/en/home/desktops/desktop-inspiron-546/pd.aspx?refid=desktop-inspiron-546&s=dhs&cs=19&ref=dthp