In short I made following experience:
Connecting the 2 PC cards Netgear WG511T and 3COM 3CRPAG175 in Ad-hoc-mode with G or B only and with WEP enabled didn't function. The cards where used with the card manufactures own WLAN software (WinXP Wlan control disabled) on two XP Pro SP1 Laptops. With WEP enabled the cards could see each other, but they didn't establish network communications. I set up the IP network and WEP keys manually.
Without WEP enabled communication works fine, but is useless for security reasons.
I was also negatively surprised to find out, that the 3COM configuration software does NOT offer a WPA-PSK option.
Questions: Did anyone succeed to connect a WG511T and a 3crpag175 in Adhoc/ encrypted /G mode?
Does the C3RPAG175 support WPA encryption?
Thanks for your help. Lophiomys