Try looking into the CAST function of SQL, if you want to do the calculations in the query.
try this (works on MSSQL 7):
select cast(REPLACE(myvarcharnumber,',','') as float) from mytable
The REPLACE strips the commas, so the value can be converted using CAST
MySQL, unfortunately, can't CAST as a float, onlyt signed or unsigned integer, which drops everything after the decimal.
http://www.mysql.com/doc/en/Cast_Functions.html