just get a cheap capacitor around RM 5, else u will blow ur tweet in no time

u need to remember to get a non-polarised one, anything above 200v will do... value will depends on the impedance of ur tweet and ur xover point

get a
5.5uF for 8ohm, xover@ ~3500Hz
7.5uF for 6ohm, xover@ ~3500Hz
11uF for 4ohm, xover@ ~3500Hz

you are pretty safe with those value. u need to get the impedance correct.

erm, wat do u need then ? if you don't know wat u need, of course it's hard for u to tell the shop assistant wat u need and it's hard for me to advice u also