I wouldn't say the AMD A64 series was "designed" for gaming, they just happenend to be better at it because of the architecture they incorporated (shorter pipelines among other things). As for the 64 bit architecture.....Well that makes almost zero difference when you are running Windows XP 32-bit, and most games out there.
Elbatrop is correct, the "faster" gaming experience you had was probably on a PC with a better graphics card, since it plays a much bigger part in today's games.
And dual core CPUs not being double the speed of single cores, is 100% correct. But with the next generation of programs and games that should really be showing up from now on, it will be better in the long run to have a dual-core CPU "under the hood".
AMD64 X2 4400+
DFI Lanparty Ultra-D
2GB Kingston Hyper-X (2-3-2-6)
TT Big Typhoon
eVGA 7900GT KO Superclocked (650/1650)
250GB Maxtor DiamondMax SATA2 HDD
Hiper Type-R 580W SLi PSU
19" Sony Trinitron CRT