I've put in shitload of HD's in Dells and a different size one shouldn't matter to the install disc, make sure it's *booting to the CD or DVD ROM drive first* in the BIOS, a lot of people think it'll do that , but the factory sets it up to boot from the HD first to save boot time. Alternate pressing F2, F12 and Delete a few times when it first boots up, F2 *should* get you into the BIOS, F12 *should* get you into the boot manager and just to be on the safe side, most manufacturers use Delete to get into the BIOS. Set the optical drive as first boot. Reboot with the disc in the drive. Then once it gets done with the Power On Self Test it'll prompt you to press any key to boot from the CD, press a key. I can't tell you how many people either miss that or just don't and it goes on to boot from the HD and then tell me that the Windows CD is junk . When it gets to the partition screen I usually create one for Windows and one to save things like mp3s or pics. Dells are like most any other comp I've worked on aside from the proprietary physical bits on some models and occasional odd form factor like the Mini ITX units, that and thier HD's & PSU's do have a tendency die a bit faster than on a higher quality unit.