Just to check (don't want to offend) but... You did pop the metal heatshield off the processor right? A lot of people don't/didn't with the k6-x processors, and if ya don't then a) using thermal paste is of no value and b) the heatsink is far less effective.

As for fans... Ya could maybe put a slot cooler fan in if ya got an unused slot. For the front if there's no place to mount a fan perhaps you could afix one to the case bottom (magnetic tape is one way to do this) near the front intake area (what ever area there is). Not the best, but if there are holes/slots in front the fan will draw "some" air in.