I recently had a chance to try Windows 7 Enterprise x86 on an old PC. Overall, quite impressed with performance.
At startup only 300MB out of total 512 are occupied. The system is clean, no antivirus or anything like that. But running smooth, so it’s still pretty good for 7, compared to its predecessor, Vista. No match for XP in this test, but it wasn’t supposed to.
Everest’s 5.02 CPU Queen gets 1500 marks. Compared to my Phenom 9500 X4 it’s 9 times less. Cannot say it was 9 times worse though. Even faster, in some interface options. Not too bad for Pentium 4 anyway. You might wanna upgrade your old laptop to 7, since it gives your more options and less effort to manage.
Despite being a new operating system, Windows 7 provides you an ability to upgrade from an old PC. There is, however, one hardware parameter of utmost importance - memory. Since you processor might not be that fast (and the hard drive either), you might want to consider installing 1 or 2 gigs of memory to have a room for applications.