Dialup here too, good advice up there, stick to dedicated servers with less than 10 players if you can. Get one of the "puff" mods so you can see if your hitting or not, highpingers need to confirm thier lead somehow and thats a good way. Dont try to sit and snipe, get out there and mix it up with em :P I find realism is better for me, less bullets to kill with so if I hit em a few times I'm more likely to get the kill
Another thing is to enable the built in lagometer so you can see when your spiking and if your getting lots of loss. Open the console and type
cg_lagometer 1
The display will pop up, remember, red is bad :wink:
Good luck!