Do you have the ETM for your car? If not visit this thread http://www.unitedbimmer.com/forums/u...-ftp-info.html
and d/l it (will help with other electrical as well). It'll tell youexactly where the relay you need to replace is.
As for the computer, you could browse www.realoem.com
to find the part#, then hit up either www.koperformance.com
(Paul there has helped me to get parts at the cheapest prices available - find a lower price show him a link and they'll beat it) or www.bmw-parts-direct.com
I've bought a few relays and whatnot there. decent prices, fast shipping. Also, while you're on my FTP you could grab the ETK and retrofit guides as well which will help with part #s and replacement items, etc.