This is soooo coooool! A thread aimed specifically at me! (Spike the football, do end zone dance)
Ahem, I am The New Guy. About a month ago, I was thinking/saying the exact same things that you are. I too, was suffering from a bad caseo of "Didn't Know What I was Buying and Got Stuck" disease. See, I bought a cheap Dell. However it wasn't so cheap a year ago when I bought it, and I'm still paying on it....and it's in about 45 pieces right now.
Don't misunderstand; the Dell was great. Not a single problem. Worked great right out the box. The problem was expandability. No AGP slot. Only one 5.25 bay in front, 4 PCI slots, a power supply that runs on 2 "D" batteries (it's quiet though) all housed in a Micro ATB case about the size of slightly bigger than 2 phone books. A year ago, I didn't know the difference between PCI, AGP, PIII, Athlon, Arid, Dristan or ...you get the idea.
I was using **GASP + BLUSH** the ONBOARD VIDEO! (Crowd boos, hisses and throws things). When I got into gaming I bought a Voodoo 3000 PCI. It was like seeing Jesus. Then, I saw my friends'32 meg NVIDIA based cards and got jealous cause I couldn't upgrade.
So, I couldn't do AGP. Couldn't have two CDR drives, couldn't upgrade my processor because the Dell BIOS lets you change all of 7 settings, and none of them count. You get the idea.
With OEM systems you're very limited as to how much upgradability you have. For the casual/neophyte user (my Aunt Marge) who only knows "icons" (Doesn't know the start menu exists...no kidding!) an OEM system is best because when something goes wrong, they call 1800-DELL and the nice man on the other end tells her the magic secrets. If you were that basic a user, you wouldn't be on this forum. I say go for it! Remember, you get what you pay for. There's a reason why 128mb of memory is an amazingly low $12.54. It's grade-D reject memory. Buy good stuff and it'll last you.
If you already have (and you do) monitor, keyboard, mouse, speakers AND an original OEM operating system, well, that's about 500 bucks saved right there. I put together one helluva system for $1,000 that'll beat the pants off any retail system costing the same amount.
Trust me, if you can swap memory, drives, cables, install software and drivers, you CAN put together your own pc. I got a whole lot of advice from this very forum, plus I work in a facility with it's own LAN shop (over 2,000 LAN drops in one building) so I had some very experienced people to ask, but heck, I did it. Nothing even blew up. Good luck!