Can someone tell me the primary differences between the Vostro line and the Precision line of desktops?

I've read all about both, and I can get what I want in either line, but the Vostro is much cheaper.  Is the primary difference the motherboard layout?  Also, can I get just a one year warranty on the Precision, and without a monitor, online, or do I have to call in?  This will be for home use, to replace a Dimension 4550 or an E510, as seen in my signature.

 

Thanks