A minor quibble first. The first boot into XP brings up two license agreements. One is the standard Windows one. The second is IBM-specific, and says:
"You must agree to this license in order to continue to use the software and hardware"
I need a license to use my hardware? The hardware I've just paid large sums of money for? Haha. But no. That's what it says.
Differently irritating. There's a blue button that causes it to boot from a hidden partition at the end of the disk. This brings up Windows 2K Preload Environment, a cut-down embedded Windows. Oddly, there's a copy of Opera included in it to let you access support sites. On the downside, it'll only work if you have DHCP (there's no way to set up static configuration) and over the wired ethernet (there's no way to use wireless in it). Anyway, there's a handy button there that causes it to write a new disk image over your hard drive (optionally only to the first partition, allowing you to resize Windows and reinstall it without it screwing up everything in the process). All very nice, and I'm sure it's excellent for the corporate market. The only real issue is that if you overwrite the MBR with something like, say, grub, the blue button stops working. Nice one.
Vastly irritating. IBM optionally ship this model with an Intel Prowireless 2100 card (the wireless component of the "Centrino" package). For no obvious reason, the packages currently available only include one of these if you're willing to pay for copies of Lotus Smartsuite as well, so are about £200 more expensive than the non-wireless ones. But anyway. As the technical specifications point out, it contains a Mini PCI slot. And I have to hand an Intel Prowireless 2100 card. IBM list the device as approved. Installing it is easy enough, and powering on the machine reveals that what was previously a "Pentium M" logo on the BIOS splash screen has now changed to a "Centrino" one.
Shortly afterwards, the splash screen is replaced by
ERROR 1802: Unauthorized network card is plugged in - Power off and remove the miniPCI network card.
It turns out that the BIOS appears to check the card against a whitelist. Despite having an identical model name, my card is missing an "IBM" from the part number. Further investigation also reveals that it has a different PCI subsystem ID. The BIOS appears to be picking up on that and refusing to work. Calling IBM technical support wasn't a desperately enlightening experience. The only thing I could get out of them was "We only support cards provided by IBM". My supplier (CEC, who have a dreadful website but seem to be quite lovely people so far) became a little concerned when I started muttering things like "Sale of goods act" and "Distance selling regulations", so contacted IBM themselves. The only thing they could get out of them was "It's a proprietary connector so will only support IBM hardware", which will presumably come as news to the PCI SIG who seem fairly convinced that Mini PCI is a standard. They've kindly offered me 50% off an IBM wireless card, but that would take 10 business days to supply (IBM is apparently dropping the 802.11b card as a separate part) and still cost £50 or so. I've filed a complaint with IBM and am waiting to hear back from them at the moment.
The real question is "why". IBM surely wouldn't be stupid enough to try to block any non-IBM parts for a reason. So far, the best answer I can find is based on IBM's FCC filings (search on ANO20020201CLK). By the looks of it, IBM believes that they can only receive FCC approval for a combined antenna/transmitter combination, and so are attempting to make sure that this is the only way in which their devices can be operated in case they're held liable.
There's the minor issue that the FCC is several thousand miles away from here, but, well.
The card will apparently work correctly if it's inserted after the BIOS screen. I've no especially strong desire to use it that way.
But honestly. I mean, Christ.
IBM is worse than Orkut.
 "Oddly" because Opera is shipped in the recovery partition but not in the main image, where you're stuck with IE instead.