How to get MacBook Leopard installation disks?
Apple doesn't technically sell operating system software discs anymore. If you call AppleCare will often mail you replacement DVDs for what shipped with the system depending on how old it is (1-800-APL-CARE).  

If you are looking for the DVDs for third party software AND you have the valid serial numbers for said programs, sometimes the software manufacturers will send you replacement DVDs.  That is as long as this system is the only one that they will be installed on.  

Otherwise you can look on ebay/amazon for slightly out of date software that may well work for your needs.  

If you need a very capable free office package you can try http://www.openoffice.org.  There are many very capable open source programs that you can use on the Mac as well: http://opensourcemac.org