On what system?
For a mini 9 you just unscrew the two screws on the bottom panel, snap it off, take out the screw for the SSD
, rotate it up, pull it out, put the new one in, push it down, screw it down, unclip the memory, rotate up, pull out, put the new one in, push it down, clip it in, put the cover back on. It's easier done than said.
Other systems are more complicated.
To reinstall Windows XP, get an external CD drive and visit WindowsReinstall.com for a tutorial on how to reinstall it. If you want to dualboot, install Windows to a partition that takes up half of the drive and install Ubuntu second, to another partition that takes up half the drive.
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