I enjoy playing sins more on my weak laptop than my more powerful pc because both experience the late game lag and sins runs well enough if u follow the general rule:
Turn off virtual memory if u have more than 3gb of ram for all hard disks.
turn off indexing for all hard disks.
Set compatibility mode to run the game while disabling windows graphics features and lowering the resolution to 640x480.
Run the game at the lowest resolution 1024x768.
use only deep backgrounds or non at all. turn off the other stuff u don't need, (looks just fine with this background alone)
use low settings and the lowest engine trails etc
Biggest maps u should play are the first half of the medium maps.
Be aggressive with your gameplay and don't turtle. Attack, attack and attack on multiple fronts as well. Don't let the enemy accumulate a large fleet.
My Laptop Specs
Centrino 2: core duo 2 at 2.0ghz
3gb ddr2 ram shared with the gpu
Nvidia Geforce 9300 GS 256mb + shared
250gb hardisk. 20gb free space now.
make sure u don't overclock the CPU 2 much... the heat will also create a laggy experience. 2.4ghz is fine for medium maps.
Get 1 or 2 more gb of ram