How do I symlink each of the files in one directory to another directory?

You can use (GNU) cp with the --symbolic-link option:

prompt$ mkdir foo
prompt$ cd foo
prompt$ touch a b c
prompt$ mkdir ../bar
prompt$ cd ../bar
prompt$ cp --symbolic-link ../foo/* .
prompt$ ls -l
total 0
lrwxrwxrwx. 1 hlovdal hlovdal 8 Jun 12 16:24 a -> ../foo/a
lrwxrwxrwx. 1 hlovdal hlovdal 8 Jun 12 16:24 b -> ../foo/b
lrwxrwxrwx. 1 hlovdal hlovdal 8 Jun 12 16:24 c -> ../foo/c
prompt$

Give this a try:

ln -s /foo/* /bar

The source directory, as specified in the question, is /foo. Note that it must be fully specified (i.e. starting at the root directory), so other examples would look like this:

ln -s /some/dir/with/baz/* destdir
ln -s /dir/to/link/from/* /dir/to/link/to
ln -s $PWD/stuff/* more/stuff

Something like this?

cd /foo
for f in *; do ln -s $PWD/$f /bar; done