The only mod for my T43 i have done is installing WiFi-N adapter. I have read this forum about preferable WiFI-n adapters and find not so much posts about Broadcom BCM43222 (mainly in T23 forum). But this is the only mini PCI adapter can use upper 5GHz band - so i have chosen it for this mod.
All things are simple. But some hints.
This adapter in "half" sized mini PCI form factor but antenna wires are long enough to connect. This adapter haven't marks for "main" and "aux" so i put gray wire to connector marked as "1" and black to "2". BIOS noticed that this adapter is not IBM-branded so mkes Thinkpad unbootable (2010 error + 1802 for my Fujitsu HDD). I have found "T43p-1YET65WW_SLIC2.1_no_1802_no_2010" BIOS somewhere in the net - burned CD and started flasing. And it have failed

at 14s step with error, but i have forgotten error code). Flasher said that i must take crisis diskette and repair BIOS. But after restarting Thinkpad have booted normally and there are no more 1802 and 2010. All seems working. SLIC toolkit said that 2.1 SLIC is present. I have tried reflashing with another CD but the same error have appeared. May be problem in wrong BIOS? Initially it was 1.29 with 10.6 EC. But i don't know MT of this Thinkpad. Initially it was T43p 2668-Y84 but mainboard have been replaced with 42T0067.
Is this BIOS correct for this mainboard? And what have happened with flasher?
After that adapter works ok. I haven't tested it in 5GHz band, but old 2.4GHz networks are working well. Indicator below LCD doesn't work at all but i know the solution was discussed on this forum.