PWP There's more to this than you seem to have heard so far. There are possibilities both under JAA and NPPL.
JAA PPL
You can train for a PPL SEP (single engine piston ie PA28 etc) or for a PPL TMG (touring motor glider ie Grob 109, T-67). Once you have either of these you only need to undergo class rating training and a skill test to add TMG to SEP or vice-versa. Class rating training is 'as long as it takes' and the skill test is 40 minutes of GH and circuits. In the UK a TMG rating will allow you to fly SLMGs (such as Stemme S10) as well.
NPPL
You can train for a NPPL on certain SEP or on SLMG (which, this time, include TMGs). You then need differences training to add SEP to the SLMG or vice versa. As Fly Stimulator says, you need to be careful about what, where and with whom if you want to convert subsequently to a JAA PPL.