I've wanted to upgrade my Inspiron's hard drive from 90G to something larger, and I notice that Dell advertised a 320G drive as compatible, so I bought it.
A hardware support guy warned me that there was a 120G BIOS limit on hard drive capacity for the 8600, so I decided to do some research. It's true, many older machines have a BIOS hard drive addressing limit of 137G (1G=1GB=10^9), or 127.5 GiB (1 GiB "GibiByte" = some power of two making it close to 1GB). Therefore (per my research) any BIOS involvement with the hard drive must address below 137G. That includes the BIOS loader, extended partition control data, and the first part of Windows' startup code, where it's still using BIOS calls for hard drive I/O. The basic advice is that Windows' C: partition should fall below this line, along with the extended partition control data, and any other boot code.
A modern BIOS would support LBA (logical block addressing) mode which would certainly handle a 320G drive. I understand that WinXP needs service pack 2 for full addressing support (LBA?), and possibly a registry patch. I decided to stay away from this for now.
Even a 130G Windows is lots better than the 90G I had before, and I decided to give the rest of the drive to Linux. I put Linux's /boot as a primary partition below the 137G point and also left space to restore the Dell diagnostic partition (when I have that figured out). The Linux / and /user partitions were allocated in the extended partition, and crossed the 137G boundary.
After a little hitch when I confused GB and GiB, I got a working WinXP partition, and shortly after that a working Linux system. There don't seem to be problems with this setup, so I guess I lucked out.
I eventually hope to put a Win32 partition in high disk space as well, to use for file sharing with WinXP. Then I'll find out if Windows uses LBA once booting starts up the kernel.
I wrote this little missive to help others with this kind of an upgrade. It's certainly not for computer newbies! I've still got my fingers crossed that there aren't any more gotcha's -- and I'm keeping very faithful backups.