Go to the Asus website. Expand the view of the mobo. Look closely to see where the mounting holes for the mobo are, also they will give the overall size of the mobo.
Then look at the case and existing mobo, note the mounting hole locations, mobo size et al. If they appear to be close, it is likely that they are using the standard ATX locations. [may have one ot two more, or fewer mounting holes] The mounting holes all have the plated copper ring around them, so should be easy to spot. If any is to be non-standard my guess would be the Compaq. They generally are a PITA.
Whatever you do when installing a new mobo in a case where another had been be SURE to not leave any mounting standoff's in that do not line up with the new mobo's mounting holes, they will short out the mobo.
You are likely to need a new Power Supply also, so why not buy a new tower sans power supply and buy a good power supply separately.
Give the old computer to someone that can't afford one.
but here goes. I've realised that I need a new motherboard, and I've found one from ASUS that sounds great, except the sales guy pointed out that it might not fit in my IBM NetVista machine. IBM didn't know if the specs were right or not, and I haven't gotten hold of ASUS. So, I figured I could move motherboard and processor to an old Compaq tower that I've got. Now the question is, will that work? The original processor in the Compaq is a Pentium II, but surely it's the motherboard+cpu that has to fit together? So if I rip everything out and then install it, would that work? Oh, and has anyone any experience with installing an ATUS motherboard in a NetVista machine?