If you need to expand your MyISAM table size for your MySQL DB becuase you simply have too much data then this is a nice quick tutorial on accomplishing your goal.
http://jeremy.zawodny.com/blog/archives/000796.html
Basically do the following
mysql> alter table your_table max_rows = 200000000000 avg_row_length = 50;
And that will increase it to its maximum size.