If you are trying to delete the preinstalled account contacts like #bal, you can't. However, you can choose to not display them. When in your contacts, hit menu, then select "Display Options". On th ebottom half of the screen are all the apps that will gather contacts together. The only one that I have turned on is Google/Systemgroup: My Contacts. I unchecked all the others listed in google, as well as any other accounts, such as Facebook, Twitter, etc. This will not effect those other services from syncing with your contacts. Their facebook status will still show up in the contact.
I also find it helpful to check off the box for "Only contacts with phone numbers"
Good luck.