My favorite book is Upgrading and Repairing PCs, but Winn L. Rosch Hardware Bible isn't bad. You can pick up an older version of either off e*Bay pretty cheap. Hell,
I need to; I'm stuck with a 3rd ed. Uprading.
I'm sure there are sites around... Hell, there's stuff these geeks post I don't understand, either, and I
am a geek. What sites are good, I don't know. If you find some, post 'em... Even if I'm not interested, I'm sure I'll run across someone who is.
But, as far as IRQ's 'n stuff, just play hard with your computer. It'll f**k up sooner or later, then fix it yerself. You'll learn the basics quick enough. If that's not fast enough, try installing a few modems or sound cards in DOS, and that'll cover IRQ's and DMA's!
For specific questions, feel free to ask me, though there are geekier people here
