The peps/SUs you need will depend on the software release of your Symposium (SCCS).
For 4.0 (4.01.07) the most recent is 40107SU11S. Get it quick, this release is now obsolete.
For 4.2 (4.02.06), the most recent is 40206SU13S.
For 5.0, there is an SU and some peps: NN SCCS 5.0 SU04 S, NN SCCS 5.0 SUS 0401 S, NN SCCS 5.0 SUS 0402 S, and NN SCCS 5.0 SUS 0403 S. (Yes, the numbering syntax has changed).
For Web Client, you'll either have version 4.0 or 4.5:
4.0 (04.00.037), it is SU08 (Build 04.02.16.04). Again, get this quickly before it is pulled from the shelves.
4.5 (04.05.00), it is SU05 (Build 04.05.005.02).
If you are an end user, you probably do not have access to the Nortel PEP library. In that case, contact your vendor, who should be able to provide this and/or install them for you.