Im not a serious gamer and mainly use my computer for photoshop and the internet. Over the years my ancient computer has received various components, including a decent amount of ram and a good graphics card, and now all thats left of the original rig is the case, the mother board and the cpu.
The CPU is only 1.4ghz, which meets the minimum specs for the game i want to play but it still lags.
I looked into a bundle deal of a motherboard and a 2.53ghz CPU but the guy at the shop said its not worth upgrading to that as "mine will run XP fine" and told me if i was to upgrade to go for the more expensive deal with the dual core 2.8ghz CPU but i dont want to spend that much as, like i said before, i dont really use my computer for gaming very often.

So to recap:
1) Is the CPU making my game lag?
2) Will the 2.53ghz CPU improve the speed of the game?
3) Is it really all that necessary to spend an extra $100 in the 2.8ghz processor?


Thanks for taking the time to read this and thanks in advance for any advice you can give.