I guess you're getting old man? Check
this post (and especially who made it

)
Hah, ok you sorta kinda got me on that, but at least N-rage 1.83a only supports MemPak DexDrive saves with the .a64 extension, while the Dex saves on that GameFAQs page are .n64. Unless N-Rage v2.0x made some changes, you can't load those save files via N-rage.
Then again, .a64 and .n64 might be the same thing (i.e. just change the extension and you're done), but I suspect that they aren't - I've never tried the switch myself.
P.S. yeah, I'm getting old. One foot in the grave.