Is 1.8GHz good enough for a gaming laptop

That is completely dependant on which games you wish to play. Chances are you will need a faster processor to be able to play games such as Gears of war 2 which requires a minimum of 2.4 Ghz. Unreal tournament 3 - 2.8 Ghz, Bioshock - 2.4, C&C3 - 2.4.

You can play Portal though: It only has 1.7 Ghz minimum requirement.

basically your not going to be able to play much with a 1.8 Ghz processor and even if you do, the games you play will probably have to be set to the lowest graphics settings and will still lag like crazy.