my pc is pentium 4 3.0ghz

1gb ram ddr2

geforce 9600 gso  

22fps 

I would suggest getting an Intel i5

A Graphics card from at least the 700 series

and getting 8 gb ram.

All of these items are budget and you can expect a good experience in other games as well. As for Raft, the game is not optimized very well, so it will still lag a bit compared to most games out there.