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
I currently have a Dimension 300 running XP Pro with a DVD recorder and a separate DVD player, it is a home computer and used mostly for emails. As a home computer it is running about 18 hours a day, although much of that time is spent idle. This is my 3rd Dell computer and it, as with all of the others has been basically trouble free.
My extended service policy runs out at the end of the year and since the computer will be 4 years old then, I plan on buying a new computer. Speed is not currently a problem, nor is the memory size, I've used less than a third of my roughtly 60GB drive now. The physical size of the computer is also not a problem or a limiting factor.
Since all of the model designations have changed, which dell computer that is now being produced will be at least equivalent to my current one for the least amount of money. When I say equivalent, I am also talking about reliability or am I better off just replacing parts that go up in my present computer or going with a competing brand.
From what I'm reading and hearing, Dell doesn't make products that are as reliable as they used to be (or do they).

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