IRQ is usually a driver issue but can also point to ram issues. This can easily be diagnosed by uninstalling whatever latest drivers were installed in safemode, then reverting to previous drivers or grabbing latest from the internet. If it's a ram issue, running memtest will tell you if a stick has gone bad.
Your NTLDR error happens when the system has a problem finding a solid source to boot from. If it randomly happens, pop in your windows 2000 cd and go into repair mode.
The problems you list here tend not to show their ugly face anymore, however. I have experienced them though, but I can say it's not as much of a headache as you would think.
Try diagnosing a faulty northbridge, then tell me how hard PC's are