I ran across this just now (I know Runar posted on it earlier; I wasn't really paying attention then). So anyway, I opened up a workspace in BottomFeeder. Two minutes later:

| stream |
stream := WriteStream on: String new.
1 to: 100 do: [:index |
	(index \\ 3) = 0 
		ifTrue: [stream nextPutAll: '(', index printString, ')', ' fizz '].
	(index \\ 5) = 0 
		ifTrue: [stream nextPutAll: '(', index printString, ')',' buzz '].
	(index \\ 3 ~= 0 and: [index \\ 5 ~= 0])
		ifTrue: [stream nextPutAll: ' ', index printString, ' ']].
^stream contents

You might wonder why I dumped to a stream instead of the Transcript - well, I was doing this in my BottomFeeder runtime, so I didn't have a Transcript to dump to :) The output looks like this - I included the numbers in front of the Fizz and Buzz so I could be lazy about checking the output :)

 1  2 (3) fizz  4 (5) buzz (6) fizz  7  8 (9) fizz (10) buzz  11 (12) fizz  13  14 (15) fizz (15) buzz  
16  17 (18) fizz  19 (20) buzz (21) fizz  22  23 (24) fizz (25) buzz  26 (27) fizz  28  29 
(30) fizz (30) buzz  31  32 (33) fizz  34 (35) buzz (36) fizz  37  38 (39) fizz (40) buzz  
41 (42) fizz  43  44 (45) fizz (45) buzz  46  47 (48) fizz  49 (50) buzz (51) fizz  52  
53 (54) fizz (55) buzz  56 (57) fizz  58  59 (60) fizz (60) buzz  61  62 (63) fizz  
64 (65) buzz (66) fizz  67  68 (69) fizz (70) buzz  71 (72) fizz  73  74 (75) fizz (75) buzz  
76  77 (78) fizz  79 (80) buzz (81) fizz  82  83 (84) fizz (85) buzz  86 (87) fizz  88  
89 (90) fizz (90) buzz  91  92 (93) fizz  94 (95) buzz (96) fizz  97  98 (99) fizz (100) buzz 

Update: Dohhh - what if it's both :)