Whats your connection speed?? this is a major factor, anything below 256kb is not really acceptible for playing.
If your running msn that shouldnt matter unless you have 512kb but sitll you are able to use msn as well on a 256kb connection.
Your hardware, a system with low specs doesnt help and gives you extremly high ping.
viruses and spyware will also slow you down heaps, try getting something like spybot search and destroy or ad-aware. (just search google for them).
I have attached a config file, (C:\Valve\Steam\Steamapps\<yourLOGIN>\couter strike source\cstrike\CFG. stick it in there, if that doesnt help just delete it and now you know that you obviously have some sort of ocmputer problem.