tl;dr - I have 4 devices sharing 1 IRQ. Is this bad and how do I tell the BIOS to stop it?

Background:

I have an old Dell GX280 dual Pentium 4 that I (semi) resurrected last weekend with an installation of Ubuntu 12.04. Everything was going fine the first several hours until a problem that plagued me when WinXP was on that machine happened -- it froze. Completely froze. None of the myriad of ways I have found here on askubuntu helped me to regain control except a long-press of the power button to shut it off. Clearly, this wasn't a software/WinXP issue.

After much googling, I found that hardware conflicts can often cause this sort of total lock-up and with all the odd blocks of yellow and flecks of color showing on my screen (both WinXP and Ubuntu) I figured my old GeForce 7600 was failing and causing me these odd issues. (A good canned-air dusting of the entire interior fixed the color fleck problem)

Again, through much googling and numerous answers found on askubuntu, I somehow stumbled my way onto the lshw command. After going through it, line by line, I found that I have four devices sharing IRQ 16: eth0, wlan0, ide0 (DVD-RW), and my video card. In hindsight, I can recall weird instances of my Ethernet connection to another computer not working when I thought it should. I never full troubleshot those issues so it could be a coincidence.

The other thing that has been plaguing me since installing Ubuntu (wasn't there during WinXP) has been periodic moments of my monitor getting no signal from Ubuntu during boot. The first couple days, it would disappear after the Dell boot screen and reappear at Ubuntu login. Now, it disappears after the Dell boot screen and doesn't return at all -- I have to hit F12 where I can load a safe mode version of Ubuntu and get more details like dmesg and lsdev. I also ran memtest86 overnight and woke up to zero errors, so failing RAM is out.

Where do I go from here?