In my opinion you could prob handle putting in a new processor, but i don't think its worth it to be honest. Your machine looks pretty old and slow :/ no offense. If it to slow for your needs, your prob better off investing a little more in a new computer
. Once again just my opinion, someone else might post a different opinion.
Product Specifications Compaq Presario S3000NX Desktop PC | HP® Support
If this isnt the same computer i linked, let me know please