Is it possible to give a hint to Explorer.exe that it's dealing with slow drive, for example, something like a network share? Explorer should go easy with it, i.e. not constantly looking up
The most important thing you can do to speed up Explorer is to disable thumnails. This limits any "automatic" access to polling the filesystem.
To do so, run
In addition, you might also want to increase your filesystem RAM cache so that XP doesn't have to keep calling the filesystem for files. You can do with with the SysInternals utility CacheSet.
And if you're paranoid, please back up. Windows XP is going the way of the dinosaur and behaves kind of like one.
Limiting 3rd party shell extensions and real time anti malware will also go a long way toward increasing Explorer's performance.