One of the best places for help that I have found has been the website located here http://www.echodelta.net/mbs/eng-translator.php The link actually takes you to the coordinates translator which, when the information is entered correctly, will give you the latitude and longitude as well as maps (including an interactive google map) of the coordinate entered.
The first thing you must do is find the specific geographical coordinate system to use. If you are familiar with where the unit that you are working with is located, it will be easy to fine here... http://www.echodelta.net/mbs/eng-overview.php
For an example, the November 23, 1944 entry for B company of the 157th Engineer Combat Battalion states “Completed by-pass and bridge repair at Grandrexange, (Q405100)”. I know approximately where they were located and after conferring with the geographical coordinate systems I can confirm that they were in the In the Nord de Guerre Zone. (luckily for the 157th, they were pretty good in identifying which coordinate system they were in) Using the coordinate translator (the first link above) you must first change the grid location to “Nord de Guerre Zone”.
The next step is to enter the coordinates. This must include two letters followed by six numbers. This is the tricky part because the 157th notes usually only contain one letter and six numbers (occasionally only 4 numbers). Based on your example, your unit did not appear to have included any letters. Again, if you know where your unit was, you can look further into the subdivided zones (shown in the second link provided) and try to determine which two letter square they were in. Since the 157th example had the letter "Q" and knowing approximately where the company was at the time, I was able to determine that the Q should actually be WQ. Luckily there are six numbers in this example so in the translator, add the code WQ405100 (no spaces) and hit convert. I have included an image of the google map showing the location being right next to an overpass in Grandrexange.
As I mentioned, it is not the easiest to use and there are a number of tricks that I have found to help when you do not have complete codes. If i recall correctly, the website does give a few hints at trying to figure out the full code but the more you mess around with it, the easier it becomes. Good luck!
Brian