I have a voodoo2 in SLI, set up combined with a MMX 233, in a closed case with no fan in it besides the one in the power supply and the one on the CPU, gaming while it is 31C outside on the attic. The voodoo2 doesn't get any higher than 62C while it is 33C inside the house.
I would not consider going trough the hassle of cooling these cards, let alone doing it on a Pentium which runs 66Mhz slower than the one I am using.
Playing Deus Ex on a Athlon XP2400+ 2GHz on these cards the other hand, resulted in a crash after 2 hours of gaming since the bottom card ceased to function due to the heat. I have put a in house fan on it due to the extreme temperatures at the attic at the moment, otherwise I wouldn't even consider cooling this setup either. Normally it will go as high as 71C when it is 20C in the room.
Xp2400+ gf3 ti200 + vd2 SLI 12MB + 768MB + SB live @ WinXP & 98 Dualboot.
MMX233 + S3trio 3D/X2 8MB + 3Dfx Voodoo 1 + AWE64 + 64MB SDR @ msdos / win98.