A lot of us are building our own systems (choosing our own parts). It may sound pricey but it's actually cheaper than buying a pre-built HP.
Example:
Highest graphics card you can get costs $300, next step down is about $160.
Motherboards range in price a LOT. So do cooling systems. Let's go with a hypothetical system.
Case: $50
PSU: $75
Motherboard: $150
Processor (3+ GHz or so): $200 (give or take, this one depends)
Highest end video card you can get: $300
RAM (2GB): $250 (thereabouts)
Hard Drive: $150 (for ~200GB)
Sound Blaster Audigy: ~$75 (?)
DVD-RW: $50
Floppy Disk (actually useful in BIOS updating): $10
So you get a VERY high end system with kick-arse graphics, RAM, and CPU, a large new HD, all for (in this case) $1310.
A comparable setup sold to you by Dell or HP, despite the fact that they bog it down with proprietary hardware, OEM software, and all that other stuff, will cost you upwards of $3000 (if you're LUCKY!).
Also, when you buy Dell, or Gateway, or HP, you have the problem of not being able to upgrade later. You can choose a case that you KNOW will take standard ATX motherboards (so you can keep the case when you upgrade in 3 years), as opposed to my old Gateway case, which had a STAMPED STEEL backplate (that, quite conveniently, only fit the motherboard that came with it). You get the peace of mind in knowing that you have a common socket type, and not the most obscure types that Dell and HP seem to favor, which never allow you to upgrade your CPU later on. You know that your RAM type is common, and not RDRAM, or takes only one special type of PC2700 (like my sister's PC).
So it's not just about saving money, it's about picking a PC with the best parts for the best price, and knowing that you'll be able to change said parts later on in life, without fear.
That's my philosophy on it. I'm not buying a pre-built PC ever again, after I found the freedom with my current (custom-built) system.