>good cheap cases
Those two words usually do not go together. I like the Antec cases (e.g., http://duxcw.com/digest/Reviews/Cases/antec/ks282.htm) and they are worth the little bit more they may cost. I get them from http://www.techstore.com/solutions/default.asp.
>what is the best method to cool a Athlon XP 1900?
With a heatsink-fan. I like the one at http://duxcw.com/digest/Howto/mb/epox/8kha/2.htm. I am sure other readers have comments on this subject. There are some reader observations already in this and the motherboard forums. Larry