I believe when it says "USB 2.0" that it really means it's
compliant with the USB 2.0
spec. In other words, if your computer has 2.0 ports, it will work at that speed when placed into the dock. Since the T23 only has USB 1.1 ports, unless there is special hardware inside the mini-dock that supports 2.0 (i.e something like a PCMCIA adapter), then you are stuck with 1.1 speeds.
Your alternatives? Use a PCMCIA-to-USB2.0 adapter. I have an Apricorn "ez usb 2.0" which seemed to work okay the one time I used it several months ago. I bought it for my 600X in order to do backups with an external USB 2.0 hard drive. There are other adapters; I wanted that particular model because it only takes up one slot (type II card).
edit: I searched IBM's site and found this:
ftp://ftp.software.ibm.com/pc/pccbbs/op ... 2p1837.pdf
It's the users manual for the port replicator and mini-dock systems. On page 7 there is this note:
"If your Thinkpad computer does not support USB 2.0, any attached USB device does not work in USB 2.0 high-speed mode"