I ordered a bigger, faster disk ( a Western Digital 250 GB, with 16 MB cache) and an usb enclosure for it:
Putting the disk into the enclosure is simplicity itself, just plug the thing on the left onto the disk, slide in and tighten two screws.
Then I used Norton Ghost 14 to clone my internal disk to the new, now external usb disk.
Afterwards I opened up the enclosure and my laptop and swapped the two disks:
I rebooted - and the laptop ground to a halt at the windows login screen. Not even a nice crash - just nothing but a soothingly (ha!) blue screen. Whipping out my trusty iPhone, I searched for the reason, and soon Google told me where I went wrong: Under no circumstances should I have mounted the new disk in Windows before cloning to it. Because Windows remembers the drive letter assigned to the disk, and when you clone it you transfer the registry as well - so when booting it searches for the OS in C:\, but assignes the old letter (in my case F:\) to your spanking-new system disk.
There is an easy solution for that floating around on the internet, that does not, unfortunately, work in my case: Boot from an Win98 bootdisk (or usb stick) and perform fdisk /mbr, which erases the disk label, so Windows does not "remember" to assign the wrong letter to the disk.
But Win98 can't read NTFS, so no fdisk for me. The newer fixmbr-thing that comes with Windows XP does not work, because it does not erase the disk label.
But! There is another way: I connected my old disk vie the USB enclosure. This had still the letter "C:\" assigned to it, so I could boot. Then I found and followed the instructions here, which show you how to reassign the letter of the system drive while windows is running, using regedit. It worked!
Now I have place for all the