My computer has been slowing down over the past few years. The specifications are still relatively recent, so I am unsure why this is happening – Intel Core 2 2.13GHz with 2 GB RAM running Window XP Professional Service Pack 3. It has been suggested to me by a friend with IT experience that Windows XP becomes clogged-up after a period of time (I think this version has been on-machine for about three years, maybe more) and that the only solution is to do a clean reinstall. That seems a logical approach but of course one has then to reinstall everything. Would the same declogging effect be achieved by doing a repair reinstall? Alternatively, if a clean reinstall is really needed would I be better moving to Windows 7, as I understand that Windows 7 Professional has a Windows XP emulator so I could still use my existing programs?

Your friend is quite correct that after a few years of operation Windows (and other operating systems) do have a tendency to slow-down. This is colloquially called bit rot and refers to the fact that over time unused files accumulate on the computer (from things such as installing and uninstalling software), fragmentation of data, accumulation of startup items, etc. Therefore, it is a good idea to do a clean reformat of the hard drive and reinstallation Windows every few years to remove all of this miscellaneous data. A repair installation will not achieve the desired effect, as this simply recopies the Windows system files back over the top of the existing Windows system files (in case any are missing or corrupted). Therefore, all the accumulated data will still remain and will not be removed. The only way to get rid of this data is to reformat the hard drive and reinstall Windows from scratch. Just make sure that you backup all of your important data before undertaking this procedure, since it will result in all data on your computer being lost.

Regarding your second question, upgrading to Windows 7 would be a good idea as the operating system has already been superseded a few times so you may wish to take advantage of new features offered in Windows 7. While Windows 7 will run on your computer, you may wish to consider upgrading to 4 GB RAM to provide a bit more of a performance boost and you should also check the graphics card in your computer to see whether it supports the advanced Aero interface found in Windows 7.

In your question you mention Windows XP Mode which can be found in Windows 7 Professional and Ultimate. This literally loads a Windows XP virtual machine within Windows 7, allowing programs not compatible with Windows 7 to natively run. I should stress that this is a last resort, because as the programs are running in a virtual machine you are potentially going to hit some fairly major performance problems (particularly if you only have 2 GB RAM in the computer). Therefore, you should try your hardest to ensure that all programs you wish to run are Windows 7 compatible, and I would avoid using Windows XP Mode if possible. Should you find that the majority of programs you wish to use do not support Windows 7 then you may wish to hold off upgrading until support is offered.