Stacks keep track of the sequence of routines called in a program. For example, one routine calls another, which calls another and so on. Therefore the origination of the term "stacked". The routines are "stacked" one upon another. As each routine is completed, the computer returns control to the calling routine all the way back to the first one that started the sequence.
0000:823aa86e is a memory location which cannot be directed related to a specific cause. It only indicates the location in memory where the dump occurred.
Since Explorer encountered an error within itself, the Stack dumped all memory information. Explorer errors can be caused by many many different reasons.
At this point, tell your friend to do a DiskScan and Defrag for starters. Reboot the computer and see how things run.
Most of the time, these types of erros dissapear with a reboot. If the error returns, then come back and we'll go into it further.
Good luck
