multiple value returned from vlookup into a data validation list

hi folks,

i am probably pushing the envelope a little too far here. i have a situation as follows:

clmA clmB
a 1
b 3
b 2
b 4
c 4
c 2
d 1

for certain reasons (i can go into details if asked), i would like to do the following.

the above values in clmA are available as a data validation list elsewhere within the same spreadsheet (different tab, though). when user select a value, say 'c', from the picklist in a particular cell, in the adjacent cell i would like the data validation list to present the two values 4 and 2 (VLOOKUP returns only the first value it finds in the array, 4). i tried to use INDEX, but got stumped because i could not figure out how to use CTRL+SHFT+ENTER within the Data Validation > List > Source.

much obliged if i can get some help on this.

kind regards.