Greetings Ariane,
Some time ago, one was able to obtain an IDES (Demonstration system) installation of SAP that could've been used for a limited time (up to two weeks). But I am unclear on whether this is still available, and to be honest, getting it to run on your computer without some practical OS administration knowledge may be difficult.
But why not try access to a public IDES system? Google "free ides access" - there are several companies that can give you access to a sandbox, open-for-configuration IDES system without any charges.