it makes no difference how you type the key, upper or lower case doesnt make any difference. thing is you cant get any online support offically as the owners have closed the site. but there is a modding community that may be able to help. so try them... http://www.moddb.com/forum
it may be that the server is now closed so it will mean the game will no longer do online play (i haven't installed it for a long time so i cant be sure of this) if this is the case then they will have produced a drm free exe so you can at least enjoy what is a great single player experience. if it exists the drm free version will be on good old games or www.gog.com you will likely have to pay for it though.
but $5 is hardly bank breaking.