New Install

I have 2 or 3 queries about my install of 7, I have just done a clean install from my disc, but it has left the back up os of xp on my dell computer, at this stage I have done all the updates and spent the time etc, my queries are, would it have been better to do the install by booting from cd and deleting the old os, (I have the original xp disc should there be an emergency) do dell have it protected so that you cannot remove it ?
Now that I have gone this far is it possible to remove it another way, without going round the time consuming loop again, and my final query, I backed up all my docs etc to mem stick, once I am happy that all is ok, is it ok to remove the "windows old" file altogether (14GB) having started the process it keeps saying that deleting certain files could effect the running of pc, but I presume these are now in my new os and would not effect anything. Many thanks P. (I am happy to write off the time spent so far if the booting from cd method will improve performance)

Windows.old Folder - Delete

Always best to do a clean install.

To clean install:
1) Clean the HD Drive, using Step one in this tutorial:
SSD / HDD : Optimize for Windows Reinstallation
than
2a) clean install with the OEM manufacturer's Recovery Disk.
2b) Clean Install Windows 7

2c) UEFI (Unified Extensible Firmware Interface) - Install Windows 7 with

Everything needed is here to get and keep a perfect Clean Reinstall - Factory OEM Windows 7.

And yes you should always boot the installer, delete all partitions as shown in steps 7/8 of the illustrated tutorial for actual install Clean Install Windows 7.

However with Dell it has a valuable hardware diagnostics which can run from the ESC boot menu key, so read about how to test that it boots and then preserve it (by not deleting the first partition only) in the Special Note for Dell Owners at the end of Clean Reinstall - Factory OEM Windows 7