Okay! Thanks for your replies.
To JW: Being unable to reboot my system after changes to the boot.ini file is a real hassle. My computer has a single SATA WD Raptor drive with the OS installed on that. No other drives are recognised apart from the DVD drive.
I've got 2 Raptor drives, the 36Gb and the 76Gb. I can have them both connected to the 2 sata ports on my motherboard, but only one is recognised at a time. In the BIOS set-up, I've got "SATA Port 0 configured as ... IDE Primary Master", However, "SATA Port 1 configures as .... IDE Primary slave" is always greyed out (or more precisely, 'blued out').
I've got no other computer that accepts SATA drives. If I change the boot.ini file and the computer does not reboot, I have no other option but to re-install the O/S.
I cannot take credit for the idea of duplicating the line with the changes before editing. I got it from here
Nevertheless, you might be right. However, I've already tried just adding /3GB to the end of the line (with a space between the preceeding phrase), and it doesn't work.
To Paul: I tried placing the /3GB amendment immediately after the O/S name, as in your example, instead of at the end of the line, and it almost worked. At least the computer booted to the stage of showing all the desftop icons, but then the fatal message, "The application failed to initialize properly ....... etc." Switching off the power was the only way I could get out of this.
To Dandill: This is a new system. Both Win XP Home and Pro include SP2.
To Jack: I failed to access the knowledge base article you refer to, but in any case your post is confusing. (The 3GB switch is automatic with SP1 and SP2? What are you talking about