Yes, basically it's what Gal51 said. Jesus said that He is the vine and we are the branches, and the only time the branches are cut off is when they are thrown in Hell, so those saints in Heaven are still part of the vine. This is the communion of saints, the mystical Body of Christ.
Oftentimes when people talk of the communion of saints, they can also be talking about the Saints in Heaven interceding for us. We can ask them to pray to God for us w/ a special intention. (This is completely different than conjuring up the dead.)
I'm Catholic, and I do believe in this.
at 5:00 PM on Oct. 12, 2010