I just got my Dell-Ubuntu E520N. :) I have /dev/sda1 = fat16 = 47 MB /dev/sda2 = fat32 = 2 GB /dev/sda3 = ext3 = 196 MB /dev/sda4 = extended /dev/sda5 = linux-swap = 2.5 GB /dev/sda6 = ext3 = 228 GB
On my PC sda1 is the Dell Diagnostics. sda2 is system recovery, grub has an option to reinstall just like from the factory. I can see how a factory-reinstall would be a wonderful feature for windows users but not so important for Linux. sda3 = boot, sda5 = swap, sda6 = root (plus all user data).
By Windows do you mean Windows XP?
My GUESS is on your PC sda1 = Dell diagnostics sda5 = windows reinstall as shipped - available thru BIOS boot (if sda1 and sda5 are OK)
If you make a fresh install of Windows from CDs I would worry that Windows will destroy all the partitions, even the diagnostics ones, so it can take sda1. I have resized ntfs partitions using gparted from a LiveCd (SysRescueCD). This lets you make room for Linux. If you try this be sure to defrag the hard drive first and after resizing boot into windows and let it run it's blue screen of fixing drive C:
First step should always be a backup of everything you want to keep. Second step understand why the 3.2 GB and 22.5 GB partitions. Does windows show both C: and D: as hard drives? What are the "drive" sizes in GB? What's on them? Does the PC have a reinstall as shipped option in the BIOS boot? see https://support.dell.com/support/topics/global.aspx/support/dsn/en/document?journalid=B47E412B13DF11DC8EE4F3814F6AFF02&docid=DC47E7957E35BBC0E030A68F27280D16
My plan would be resize the 22.5 GB partition to 14 GB and create a 0.5 GB partition for swap and an 8 GB partition of ext3 for Ubuntu. If you have 6 GB or more free, it should be possible to resize and install.