Older systems have to be patched.
Another issue for building is that you need quite a bit of free disk space. Thereafter you'll need enough space to install the newly built system on. If you don't succeed rebuilding your kernel and booting up because of one reason or another there is one more strategy. Another thing to remember is that, on the venerable Intel platform, IDE drives are numbered before SCSI drives. If it still doesn't work after trying to use nocompat and you get a 'Could not open initial console' error message.