Problem solved!
The old Xircom card was a 16Bit card
The newer Sweex card was a 32Bit card.
So I guess the ancient laptop couldn't handle this, and the 32Bit card didn't revert to running in 16Bit mode.
I bought some identical 3Com 3CCFE574BT 16Bit 10/100 pcmcia adapters
and all seems to work just fine now.
The laptop has been running as my main Freesco (with 0.3.

for about a week now.
So thanx for all the support guys,
as always, you are the best!