Using the two links provided, the workstations are similar but the Dell has 8gb memory and a 1TB hard drive. The HP had 4GB memory and a 500GB drive. However, the offer price for the Dell shows £389 and the HP shows £360. Drive size probably isn’t that important between the two, I would always go for better memory but the cost of purchasing additional memory might offset.
I have used both HP and Dell for major business solutions — servers, laptops, and workstations.
I like both brands and I haven’t nec. seen one outweigh the other in performance. However, because of mgt. and purchasing familiarity, I have dealt with Dell more often than HP.
Both MFGs also (usually) have easy to replace, compartmentalized internal hardware. What I mean is that you don’t have to unscrew much to access, say, the hard drive, the CD drive, memory, etc. Most have devices that slide or flip out of the way to allow access to hardware.
One minor thing I have seen regarding business PCs/laptops is that the Dell usually has less OEM junkware than HPs. I only leave on OEM software required for devices (drivers usually). I remove all other OEM software, encryption/security, backup, update, toolbars, etc.
With all that said, if you are already in an HP environment, HP works well for you, you are familiar with it, and their support is good, I would stick with HP. It is a time and cost saver to have a complete OEM matched device (PCs or servers or switches, etc) environment and when some of your out of warranty devices go bad, you can keep them around for spare parts.
Did you mean, when you wrote Win7XP Pro —> Win7 and XP Pro?
Although you didn’t mention it, I am sure you know that 2003 server is approaching end of life within a few months as well.
Hope that helps
@HP @Dell_Technologies