We have a legal program that USES SQL express 2005. Somehow the company is saying our database has become corrupted and needs to be sent to a company to be rebuilt or fixed. The database sits on an external hard drive. We had to reload windows on the machine that it sits on. when we tried to reattach the database afterwards, we couldn't. Is there a cheap or software out there that I can use to fix it? I can't help you in regards to fixing the database but would suggest regular backups in the future to guard against this happening again. If the database gets updated frequently, it may need to be backed up daily in ORDER to prevent losing data.

Good luck in recovering the database. So you have only the .mdf and .ldf files?
The only thing left to try is:
1) take a copy of the ORIGINAL .mdf file (it's far better if it's the file as it looked BEFORE you attempted to attach it -- the attach attempt itself will modify the file)
2) if the db has only the one primary FG, attempt to do a "sp_attach_single_file_db" on the file.
If it has multiple fgs, primary and one or more secondaries, you will have to use CREATE DATABASE ... WITH ATTACH_REBUILD_LOG

For example, select "New Query" from withn Express, then issue this command:

EXEC sp_attach_single_file_db 'Db_Attach_Test',
'x:\path\to\primary\data\file\primarydatafile.mdf'
Of the programs I can recommend to you SQL Server Recovery TOOLBOX if the above suggestion don't help. I hope everything works out for you. http://www.oemailrecovery.com/sql_recovery.html
Also have a look this Recommended actions
http://itknowledgeexchange.techtarget.com/itanswers/it-seems-our-sql-database-is-corrupted/