I don't know if you are referring to an idle or a full load temp, but the temperature that you stated is not a problem for the 1800XP. According to AMD, thermal failure would not occur until 90C is reached.
Generally speaking, if you are not experiencing any lockups, then the temps are OK for your system.
My 1800 generally idles at 41C and hits 49-50C under a heavy load. That said, you may have some other case cooling/CPU cooling issues to explore, such as replacement of the retail HSF or additional case cooling capabilities.