sorry if I might be out of line here seeing as how I havent been online in a while but figured I would contribute whether good or bad.
I too have an x300 (your brother laptop) at 1.4 which I use daily. If you intrested in using one of these I probably wouldnt do it. I have taken mine apart probably 5 times in the past 3 years for servicing, you must know the heat transfer isnt very good at all and the fan is not very efficient. The OEM drive failed so upgrading to a 5400 made the system boot a few seconds sooner and increased program load time a tad but not as much as a 7200 although with each speed increase, you lose battery time.
Other than cooling issues, I and other people in forums, have had problems cloning the laptop screen on an external monitor on the 82852/82855 chipset along with other problems so see if you are using that intel chipset and make sure you can clone the desktop before going further. A stripped lite version of xp will keep your video from lagging when RR and winamp or whatever is running but not with a full xp pro install unless you have a non-oem harddrive. I've used 98, NT, XP Home/Corp/Pro, Ubuntu and OSX 10.2.8 on my x300 so I am not ignorant to the topic.
The laptop should be able to boot just fine without a battery installed but the charger needs to be kept off of carpet or cloth as it will extremely overheat and malfunction. These are still $20 w/ shipping from ebay.
Make sure to make a hard drive image once you get it setup (if you plan to) so you can restore quickly on the fly if there is a problem. I think you have a bios limitation on disk size but not sure, might want to check into flash upgrades to make sure its current.
Hope it helps someone some. Goodluck!