If you want to write your own wrapper app look at winepath for doing path conversion. We have some internal wine APIs for translating win32 to linux paths:
LPSTR (*CDECL wine_get_unix_file_name_ptr)(LPCWSTR) = (void*) GetProcAddress(GetModuleHandleA("KERNEL32"), "wine_get_unix_file_name");
You can continue this way but personally I wouldn't write a wrapper. Just register the .doc extension or whatever extension you want in the registry to winebrowser as mentioned in the FAQ (the FAQ describes it for .pdf). Wine should be able to load .doc files then if you would use 'wine start filename.doc' or from winefile, it also works from various win32 APIs.
