There are many powerful open source projects. Here is a really good site that links to many of these programs.
http://www.osalt.com/
You can replace say Photoshop with
Gimp and Audition with
Audacity for audio manipulation. The list goes on and on.
Honestly I miss nothing after switching to
Open Office. The programs can open their M$ counterpart files and can also save in M$ formats. You should take it for a test run...just install it and don't make it the default program for M$ files until you decide to remove M$ from your life.