question: PC Cooling Fan

I have an old 550mhz computer, 192 PC-100 SDRAM, and recently I have upgraded the video and sound cards (NVIDIA Hercules II MX 32MB and Creative Gamer X 5.1 respectively) Upon installation I noticed that the computer has a wee little fan toward the upper rear of the case. Now I have these 2 new improved cards for the system which probablly generate more heat. Question is do I need a new PC cooling fan? I have seen the ones that go in the PCI slots and was curious if this move is truly needed. Also, where or what do I plug the fan into...I have seen 3-4 pin cabled fans for the expansion slot.

Any advice would be truly appreciated :)

Thanks

8100 @ 1.4Mhz
256MB PC-800 RDRAM
40 GB HD
NVidia Ultra 64MB
SB Live!
X6 DVD
Windows ME
19 Trinitron