Just found your post about tracing someone in the army.
Despite Gordon Brown's best efforts, the army is still a fairly big club, so you're chum should start by establishing what regiment or corps the relative enlisted in, and also as much further information as he or she can garner. The enquirer should start by questioning the soldier's immediate next of kin. His parents, brothers, sisters etc. They may very well know much more than the enquirer. The next step, once armed with all the information gathered, would be to contact the appropriate regimental headquarters, via the internet or by telephone or better still by mail, and to seek their advice.
For obvious reasons, however, they may or may not be able or indeed willing to disclose any information before establishing just who the enquirer is. Indeed they may very well be forgiven by law to disclose any information to anyone unless he or she is a direct family member.
In the final analysis, they may merely direct the enquirer to the army records office.