How good idea is to swap my new Acer aspire laptop with my sisters old Hewlett pack Compaq?

That's one weird suggestion. Well it all goes on the user which is you, what do you want? If you are totally fine with giving in your new laptop to swap with the old one then fine and I'm surprised that the old laptop can run games on max and yours doesn't however this is more of a specifications thing. If you are satisfied with the performance given by her old laptop then go for it!

If you want more help then give me the specifications for both the laptops? The links you provided didn't work for me.

I would strongly encourage you to look up some benchmarks so you can compare the specs. Especially with their graphics processors. Passmark is good at having laptop graphics speed measurments.

But here's an example for the CPUs:

http://cpuboss.com/cpus/Intel-Core2-Duo-T7500-vs-I...

So the processor on your computer (The Acer) is easily twice as fast as the HP's processor.

The graphics is going to be the deciding factor though, and the specific adapter is hard to find through Google.

I'd suspect your missing something like the power setting on your laptop that is keeping it from playing games at max settings. You sure you have it set to full power?

It didn't seems like a good idea