This is only relevant if you erased the existing partitions, since there was a suspend partition initially. So far I haven't been able to actually get the system to hibernate, so maybe creating this partition has no use. Anyway, here's what I did.
Dell conveniently specifies the required size for this partition as Memory + Video memory + a bit extra, without telling you how much "a bit" is. Since there was originally a 141MB partition, I chose that size, meaning "a bit" is 5MB. Under RedHat, to have any control over the partitioning, you must choose "custom installation". Note that you need to use fdisk rather than diskdruid, because the latter does not let you create primary partitions.
To format the hibernate partition, you need to get rhs2d.exe (sic) from Dell's web-site. In theory, that should be easy to find, but in practice Dell's search engine often returns invalid links. One place is
http://support.euro.dell.com/de/de/filelib/download/index.asp?fileid=R22768The exe file is actually a zip file. After unzipping, you should copy the s2d.img to a floppy, by doing (as root) "cp s2d.img /dev/fd0" (not to the mounted floppy file system), which can be done by running the setup.sh script. This creates a bootable floppy. (You could also create this floppy using Windows before erasing Windows.)
Boot the laptop with the created floppy. Run the included fdisk to delete the hibernation partition. This is because a "free, unallocated, primary partition" is required. Here's where I went wrong: the floppy contains two programs, phdisk and mks2d; I couldn't find the document that purportedly would tell me which to use, but the README suggested phdisk. Wrong! While running phdisk works fine (I specified size 144384kB =141*1024, which made it happy), this is not what the BIOS expects. If you try the key sequence Fn+A it will tell you so (Fn+A apparently forces hibernation).
However, now I'm stuck: I've tried to run mks2d, but it gives me an error: Disk read error checking media descriptor byte. I have no clue what that means. A partition is created (type 0x84), but whatever needed to happen didn't apparently. If I try Fn+A now, it gives an error message about the BIOS not being compatible with mks2d. Yet various people have reported on the web that mks2d worked for them. (E.g., http://theory.gsi.de/~vanhees/dell-inspiron.) I've tried removing LILO, but that didn't help.