All Cardbus cards are going to be 32 bit.
I did some checking and, as Cobalt states, you should be able to use any type I, II, or III Cardbus (32 bit) or PCMCIA (16 bit) card with no problems (Tech Specs for Latitude CSx H
Due to changes over the years since the Latitude CSx was introduced, I would still recommend testing the card you want with the system before buying one, however. I my years working with Latitudes and wireless networking (4 years here at Dell) I have see a number of occasions where what works on paper just doesn't work in practice, but might be fixed by an update.
If you had any questions about the Latitude system feel free to contact me. I will be more than happy to help out in any way I can.
Dell Customer Advocate