I say build your own. It's easier than you think. I've always built my own PCs. There is nothing confusing about it. You could spend $1,300 on a nice desktop and pay $600 of it in labor costs. If you take that same $1,300 and build it yourself, you'll only need to upgrade your software for the next 2 years.
Its almost impossible to mess up a self built computer. Everything only fits what it's supposed to fit into. You can't stick the RAM in the video slot and vice versa, it won't fit.
You can also choose a case that will let you upgrade at will, so you don't have to buy a new computer everytime you want to upgrade. Here is my suggestion.
if you have $600 to invest in a computer, the following whould give you a very nice start. If you have more, check out CPU magazine, they have all the lastest stuff if you want to spend $7,000 making a super computer. I don't know what you are using it for so here is what I suggest.
Graphics card (128mb or larger) $50
56k modem (optional) $10
tower case ($30 - $40)
AMD Sempron 2800 + combo board ($117)
AMD is way better than pentium because it allows for over clocking and you can always just upgrade the chip without changing the board out.
512 MB RAM ($45 per stick) or
1 GB RAM ($100) a better investment
16x DVD-RW ($45) get two if you want to burn a lot of DVDs and CDs
40 GB Hard Drive ($40) you can get bigger if you need it, or put in an extra hard drive all together.
7 in 1 card reader (for digital cameras) $20
Firewire Card for Video Camera Hook Up ($30)
Windows XP ($60) depending on the version
keyboard and mouse ($20)
Monitor ($40) for a older monitor
Grand Total = $517
This will get you a good starter computer. when you upgrade, you can do it one piece at a time. I'm not sure about your area, but here you can sell the parts to a custom computer store. For example, here they give $30 for 512 RAM. You could use some of the money to upgrade your computer as you go. I do it a lot, trade in an older piece for and use the money as part of the purchase for something new.
Hope I helped.