the problem with the pumpkins is that they use a massive amount of fx... for example all of siamese dream was constructed by billy, in a studio so its anyones guess what he used. its all layered like crazy anyway...
all i can say on mayonaise is that he used a tiny little crappy cheap guitar that whistled everytime he stoped playing. thats why you get those out-of-tune note in the pauses...
anyway i might be able to help more with more spesific songs, they just use far to much equipment to be general sorry. ps. what SMPU stuff you got? i havn't met anyone on here who worships them as much as i do yet...
Tandem Felix