The latest ADE I can see is ADE 2.0 (http://www.adobe.com/uk/products/digital-editions/download.html)
It does not support XP before SP3, and lots of people have problems with it an XP SP3 as well.
It has lots of bugs even on operating systems where it does work.
There are lots of bugs in ADE2.0. Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
http://helpx.adobe.com/digital-editions/kb/cant-install-digital-editio ns.html
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172