Ricoh and earlier Hoya/Pentax discourage the use of adapted microSD cards.
What firmware version is installed on the camera - press the menu button while powering up the camera, the version should be displayed on the rear LCD. You need version 1.02 or higher for support of cards larger than 1 GB. Sort of a Catch 22 if you don't have smaller cards and you need to update from earlier than v1.02 The latest is v2.03.
I suggest you purchase an SD card of 1 GB or less (if you can find one).
You may have to go into the setup menu and change the Transfer Mode to either PC or PC-F in order to connect the PC or Mac. You do have the appropriate cable?
Firmware and user manual downloads from Ricoh Imaging Japan:
Software Downloads : Support & Service | RICOH IMAGING http://www.ricoh-imaging.co.jp/english/support/man-pdf/istds.pdf
Please make sure your battery is fully charged or you have an AC adapter connected before attempting to update the firmware.