performance of text indices

Hello,

i need some advice with indices. Normally i use autoincrement integers
as primary keys / indices for joining tables.

Now i need to create a new DB Design with 3-4 tables which will be once
filled with data i get from another persons and have two options (after
creating only reading will be made):
1) easy way for me and the other persons: using varchar fields (mostly
4-8 chars)as primary keys, so the other persons can easily handle
relationship between tables and i can "copy" data easily.

2) the hard way: i have to write several scripts to convert the data
from the other persons to keys/indices with integers.

Are text indices slower than integer indices when joining tables?

Many thanks
Daniel