The latest release is Corel Paradox 12, but, wait, that's not true: the latest release is 11, since the 12 is only eleven renamed, and, no, wait, even version 11 is substantially identical to version 10...
So, the latest REAL release of Paradox is V 10, and i think that can be ONLY bought in bundle with WordPerfect Office 2002 Pro (v 10), but you can try contacting Corel on buying a licence for Paradox only: i haven't been successful, 3 months ago, when i tried to do this for a v12 license, but you might be luckier...
And, no, neither 10 nor 11 nor 12 are "built for Windows XP", but i can assure you that i'm using version 10 with the SP3 and it runs flawlessly on my Windows XP Pro SP1, and i've been using this config for months...
Bye!