Hello Craig,
For the NW Admin exam you don't need to have 3 system landscape as training systems.
Instead you need an ABAP and a JAVA system. You can install one ERP and one NW JAVA. There are questions about JAVA systems also in admin exams.
For the all topics check the training.sap.com page and search for the exam code. Here is an example page link for C_TADM53_70 SAP Certified Technology Associate - System Administration (MS SQL DB) with SAP NetWeaver 7.0
In this page you can see the percentages of the topics for the exam. Start from the top one and study the topics.
You can see links of blogs etc at the bottom of the page for preperation. eg: How to Prepare for a Certification Exam in 5 Simple Steps
For some exams ther could be link for sample questions also.
Regards,
Yuksel AKCINAR