How can I tell if I have the "Corporate" version installed?

Insert your Windows XP CD
2. Open Windows Explorer, then navigate to: D:\I386, click 'Setupp.ini'

Note the last 3 digits next to Pid (process identifier). The three digits signify:

xxxxx335 = Retail (A boxed (By Microsoft) Windows product purchased from a retail supplier.

xxxxx270 = Volume License. Which means this version has multiple copies for larger organizations.

xxxxxOEM = Original Equipment Manufactures who resell the Windows product using their own logo's.