Find out if a PC has a TPM chip installed?

I don't know if this works on Windows XP (it does on Vista) but from here there appears to be a Control Panel for it, at least on Vista. I'd hope the same is true for XP but I have no way to verify it.

Click Start, click All Programs, click Accessories, and then click Run.

Type tpm.msc in the Open box, and then press ENTER. 

Doing this shows me this window.

Otherwise as atroon advised it may show up in either the BIOS or Device Manager (detailed here)

First, when was the laptop made? If the computer was built before 2006, it's very unlikely to have a TPM installed. If it was built after that, the first wave of TPMs were in corporate PCs like Dell Latitudes and IBM (soon to be Lenovo) ThinkPads.

From what I understand you will see an entry in the BIOS if there is a TPM installed. Another place to check would be the Device Manager in Windows, it's possible it would show up there as a hardware device, but I'm not certain.

Other than that, I would look for original documentation on the device, but I don't have any that I can find in the laptops near me. Good luck!