The answer is no, it wouldn't be "safe" to give your PC away. Even after a format. The data needs to be overwritten at least once.
My advice would be take the data you need, put it on an external HDD. Reset to factory settings.
After resetting to factory settings. Use Clonezilla
To clone your HDD, simply using DBAN, will wipe out EVERYTHING.
If you want your PC to be sold with the OS it came with, you will need to use Clonezilla first. Unless of course you have recovery CD's already.
Be sure you have before running DBAN!
If you'd like any help with it, let me know.