What's you current video card. I think my dad has a 4600 dimension, which came with a 15inch LCD and it has a plain Geforce 4mx, which is a sign that it has an AGP slot where the card is in instead of a built in video card that removes the AGP slot to where you can't upgrade.

 

So if you don't have an AGP slot, it might be hard to upgrade, but it's still possible with the use of a PCI video card, if you don't plan on gaming and may slow down the desktop a bit.

 

Here's a card if you don't do any gaming:

http://www.newegg.com/app/ViewProductDesc.asp?description=14-140-022&depa=0

 

It's $50, has DVI and VGA, so you can then connect both your new LCD to the DVI and your old 15inch LCD to the vga and have dual screens, so you can drag things over from screen to another. Very usefull when browsing many pages or want your e-mail on screen as you browse on another, etc.

 

Newegg is a good site, on of the best to deal with, I bought every part of my machine there. You can't go wrong with their customer service and fast shipping.

 

To double check if you have an AGP card, right click on your desktop, go to properties, then the settings tab (last one) and where it says Display, then what ever screen then the last part says will name the display adapter.

 

Also, if you monitor connects to a vga port that's located where those openign slots are near the bottom of the case, it's most likely a video card in the agp slot.

 

Here's a PCI version just for looks, but you want AGP if you can as that's the slot designed for videocards:

http://www.newegg.com/app/ViewProductDesc.asp?description=14-102-449&depa=0

 

Installing a card is pretty simple. Uninstall the current video drivers and anything else to do with the video card, especially if your going from nvidia to ati, but no real serious.

 

Shutdown, disconnect your monitor and the power cord from the PC to the outlet, and maybe any other powered devices connected to a usb port, or basically unplug everthing from the machine.

 

Locate the video card, take the single screw out holding it. Then unlock a plastic white latch holdign the card in the slot, pull the card out. Insert the new card, lock the latch, put int he screw, close the case, reconnect everything, start up the machine, which will be in low res low color, put in the cd that came with the card and install the drivers, restart and voila, your done.