To answer your question directly. Here are the following specs you need to have in your XP to play Lord of the Rings Conquest: Here is the address for all the information:
http://www.videogamesblogger.com/2009/01/06/lord-of-the-rings-conquest-system-requirements-of-your-pc-specs.htm
SP2 or Windows Vista (SP mean service Pack) For XP there are a total of 3 service packs. You might need to up date your computer.
* 2.4 GHz Core Duo processor or equivalent
* 1 GB RAM
* A 256 MB Video Card, with support for Pixel Shader 3.0 - nvidia 7800 or equivalent
* The latest version of DirectX 9.0c
* A DirectX 9.0c compatible sound card
* At least 6 GB of hard drive space for installation.
As far as Windows Vista these are the facts and my personal opinion.
I would stick with XP. Vista has had many problems. Vista may also not support your printer, scanner or software like quicken or commuincation software. Its been more than quirky to say the least. Here are some very important must read articles about Windows Vista. It will enlighten and educate you and Im sure lead you to a decsion of staying with XP. There is an old saying. "Dont fix what aint broke." Here's the links.
http://news.cnet.com/8301-13924_3-10149662-64.html
http://badvista.fsf.org/what-s-wrong-with-microsoft-windows-vista
http://www.pcworld.com/article/153295/skipping_windows_vista.html?tk=rss_news