date problem

Hi,
I have learnt a lot over the last week with your friendly help and it has been making my life a lot easier.

One more I am trying to solve and looking again for kind help.

Our database stores dates like this:

100001 where 100 represents year 2000 and 001 represents the day of the year.
In this particular case it is 01/01/2000.
100002 would be the second of January 2000 and the year before would have been 99001 (01/01/1999).
I would like to convert 100001 to 01/01/2000 in excel but I don't know how (Macro or Formula) whatever is easiest.

Thanks a lot
Andonny