802.11g is a lot faster than 802.11b. Nothing to do with the host interface.
Definitely not.
Yes.
Does the Pismo have only a single Cardbus slot? If there were two, I would say just get a CF card & adapter sleeve and call it good.
An internal one? Yes, you can do that: there are ATAPI CD bay to SATA drive adapter/mounting frames on ebay for ~$15. Alternatively you could use an ATAPI to CF adapter and CF card.