You do this by creating 'Artifacts' and artifact dependencies.
If project A is dependent on project B, then you create an Artifact on project B using an artifact path like so:
bin/Release/B.dll
Then on project A you setup a artifact dependency on B with path like:
B.dll
And set the destination path to be where ever project A is expecting to find B.dll e.g.
./Libs
You can do other cool stuff like automatically archiving all your artifacts into a zip by using the syntax:
bin/Release/*.dll => B.zip
and access them via:
B.zip!B.dll
All these paths are relative to build directories so makes it easy and you dont need to worry about the TeamCity guid folders or use absolute paths.