Yeah, we're going to need a bit more info. Are you referring to an Apple-branded monitor? If so, they don't come in the 24" size. Or is it another brand like a Dell?
As és mentions, the only 24" "monitor" Apple sells is the iMac, which is an all-in-one computer with no simple way to connect other computers or devices to its display. There are some third-party hardware solutions you could try, but nothing ideal.
If you are in fact referring to a 24" monitor of some sort, chances are it would be compatible with your PC. Recent Macs use DVI connectivity, which is pretty common in PCs as well. But without knowing more specifics about your PC and monitor, it's hard for anyone to say for sure.
If you really want to connect both a PC and a Mac to a single display (and possibly keyboard and mouse), take a look at a KVM switch that will enable you to easily switch back and forth.