So I tried to search for EUE files in XP and as you said it dosn't work. Hmm, that's surprising, the Win 98 haven't got this problem. You can now do 2 things: reinstall XP to W98

, or change windows register

.
In XP the search utillity is able to search keywords only in files, which the system know (as document I suppose). If you haven't fear of changing register, do this (I tried it and it is safe):
1) run REGEDIT from c:\Windows
2) open HKEY_CLASSES_ROOT on the left side
3) you can now see a list of all file types (still on the left side)
4) find .inc file type and (if is '+' before the .inc) open it
5) there should be a folder named PersistentHandler, click on it
6) right click on the line in main window and select CHANGE
7) copy the value by Ctrl+C and close the dialog window
8) find the .eue file type and click on it
9) right click on the line in main window, select change
10) delete the value there and click OK
11) right click on .eue and select New -> String value
12) name it as PerceivedType and right click on it, select change
13) as value write: text
13) right click on .eue and select New -> Key
14) name it as PersistentHandler and open it
15) right click on the line in main window and select change
16) as value paste the value you had copy from .inc (it should looks like this: {5e941d80-bf96-11cd-b579-08002b30bfeb})
Now the .eue in your register should look like this one:
17) close REGEDIT and restart your PC
Icons of EUE files will look then as icons of TXTs.
Windows search is now able to find any keyword in EUE files.