Upgrading a Dell Dimension 3000

Hi, what do you want to do with the computer? Game? IF so you need video.

Your specs: Intel® Pentium® 4 processor that runs at 2.8 GHz , 3.0 GHz, and 3.2 GHZ
With no AGP slot on the MB. (no PCIe either, that came after this generation.. this gen used AGP for video)

You cannot upgrade this computer, there is no way to plug-in better video because no AGP slot.

Good news, for $300 you can get a gaming system: for $189 get this
Core 2 Duo E6400(2.13GHz) 1GB DDR2 80GB HDD Capacity Windows 7 Home Premium
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
For $110 get this: AMD HD6770 video http://www.newegg.com/Product/Product.aspx?Item=N82E168...

what about if i switched the motherboard could i do that for a cheap fix? And then just plug in some more ram, and another hard drive and maybe a older graphics card?

You could replace MB with another p4 compatible MB. Price it out. It won't make sense. At the end you'll have a working P4 system with improved, but not good, video. That's not worth much.

If you upgrade MB, you should also upgrade CPU and Memory. At this point there's not much left from the Dell system. Again, price it out but a refurb system will be cheaper.

You could drop in an E450 fusion based MB, CPU and video for $100-$150 total, but that's not much better than the P4 and you cannot upgrade the graphics.

You could drop in an A6 or A8 fusion based cpu, mb, memory, but now you are well over $200.

Good luck.