If the disk says "Operating System", then it's Windows. They are slightly modified, a vanilla Windows XP will not detect all SATA drives, and in those cases, relevant SATA drivers are included on the CD. There's also some Dell branding and of course the automatic activation. Other drivers are not included, save the basic Windows drivers (e.g. VGA video, some older NICs, etc will be there, but your hardware probably will not have drivers).
If it says "Software Restoration CD", then it's basically a Norton Ghost image of your system as shipped. This will include trial software and such, but it also includes all the drivers, and is easier and faster to reinstall from for most people. (This is not sent by default, but if Dell support decides you need to reinstall, sometimes they will send you this. Usually I send the generic OS disk, as the SRCD is not useful for nondestructive repairs of things like filesystem corruption and boot misconfiguration.)
The disk that says "Drivers and Utilities" contains the drivers that are not necessary to boot the system.
Vostro A90, 16GB SSD, 2GB DDR2, US-INTL Keyboard, FreeBSD 7.2-STABLE
Latitude E6400N, 2.4GHz, 4GB, 320GB, Opensolaris 2009.06 updated to build 118 Dell Tech Support agent