Look at lowering the domain requirements from NTLM to whichever is the lower one. You had to do this for win98/ME clients on 2000 domains back in the day. I think the ad client add on helps or circumvents that option. (Domain Security Policy)
I would look at migrating that computer into a vm so you can get good backups of the whole thing and keep it on newer hardware .. just my .02 ~ Finally, powerful endpoint security that ISN'T a resource hog! ~ ~ <http://www.sunbeltsoftware.com/Business/VIPRE-Enterprise/> ~
