There are scads of 16 bit 10/100 PCMCIA NICs on the market. The 16 bit NICs are a bit slower than the 32 bit. Both are constrained somewhat by the bus structure of the laptop. The tradeoff for power efficiency and portability is performance.
It was just in the last year or so that CARDBUS (32 bit) stabilized. Xircom (I think)pulled their whole line of 32 bit RealPort NICs in the spring of 2000 because of bus problems (according to several techtypes at various computer organizations). Some of the LINUX releases (like RH6.something) had problems with stability of CARDBUS NICs.
If it's a new laptop, you're probably OK with the 32 bit, if the laptop is over a year or so old, you're probably much safer with the 16 bit. As I mentioned above, there are many 10/100 NICs with 16 bit interfaces. Find one from a name you trust and have at it.
FWIW
Good Luck
Scott