The thing about HPs and Dells isn't that they don't work. It's that they don't upgrade. They go out of their way to make proprietary hardware so that you have to go out of your way to get compatible parts if you want to do anything to them.
Sounds like it's not a big deal, right? Only my family had 3 HPs once. They had very low RAM as default, and we tried to get more for one of them. Nobody had it. We had to have it ordered from a compUSA or a Best Buy or something and then wait for it to come in. Then it was very expensive. We ran into similar problems down the line trying to upgrade the other computers, only the RAM we got was bad, so we had to wait even longer for more.
[Edit, left out the word "nonstandard" in the following sentence. Fixed.]
They go out of their way to make these things nonstandard: cases, fans, mounts, plugs, and a lot of other things. If you do get one with an AGP slot (or PCIe nowadays) you can stick a video card in it, but that's the one thing they CAN'T make proprietary, because nobody would make anything for a custom-format AGP slot, or a custom-format PCI slot.
Anyways, I tried to upgrade my sister's PC. She had a Dell. It was too old to simply pop in another chip, so I swapped out the motherboard. Only the case wasn't standard ATX. The fan placement for the vent out the back was nonstandard, oh and it was missing some of the screw mounts for standard ATX, and the case pins (pwr, LED, HD cables) were non-standard and I had to cut them apart and manually re-attach them to the proper mobo pins.
Hell they went out of their way to make the standard USB header had an extra row in it. Yes, it should have 1 row of 4 and 1 row of 5 pins. Only they added an unused row (without pins -- just a gap) so that only their case would work with their motherboards. Further they switched the pin order around IN that plug. I had to chop the front-panel US plug in half, grind the excess plastic down, and reverse the plug halves left to right (at least they used universal USB colors on the wires).
These folks are paranoid. They don't want you to do anything, ever, with their stuff. They want you to turn it in and get a completely new machine at the first sign of trouble. We all see how well that works for Macintosh, don't we?
So, yeah, if you're just going to use it and nothing else, they make a decent PC. If you ever want to do anything that involves opening the case, get something else.