I have a small *.vbs file, which uses the lame engine to decode mp3s to wav. simply put it somewhere on your harddisc, open it with a text editor, edit the path to lame.exe, put a link to the file into the sendto folder. now everytime you want to decode an mp3 file, rightclick on it and sent it to the vbs file. the vbs file will contact lame and lame will decode it and put the wav file into the same directory. very comfortable.
but: one serious problem remains: if an mp3 file is corrupted, many decoders have problems with decoding. e.g., I downloaded an audio book which consisted of 29 mp3 files. I don't know, who encoded them, but they were in really bad shape: some of them couldn't be even played, and most of the programmes, incl. the lame.exe couldn't decode them. I managed to decode most of them using sound forge 6. but even sound forge failed with some of them. then I went to the web and searched for some other converters. I found acoustica mp3 decoder, which successfully decoded those mp3 files, which sound forge, winlame, lame, razor lame and realjuke box 2 failed to decode. so you see, there's no perfect solution. you have to have several programmes, and try all of them, because if an mp3 file wasn't encoded properly, most decoders will have a problem with them