Many PCs, even old pentiums, say the CPU speed during bootup on the BIOS screens. Does it say on that one?

If you have a recent version of DirectX installed on the PC, running DXDIAG will tell you the speed.

If you have Microsoft Office installed on the PC, open up Word for Windows, select Help/About, and hit "System Info" (although this is going to depend on the version of Word). On my system that tells me the speed.

There are also speed-test utilities, but I don't have a link to any of them.