wondering about hosts file in windows

For the past while, I've been noticing that my linksys router seems to blink it's activity lights a lot more than before. So I went in its settings and turned on access logs for a while and noticed a fair amount of extra activity to ad sites like ads.msn.com, feeds.msn.com and many others.
I also run a zonealarm but need to have cookies turned on for a variety of sites and so these ads come through :(

Anyways, I searched around and got a few different ads lists on the net and updated my hosts file with entries like 127.0.0.1 ads.msn.com.

My host file now has maybe 15000 entries like that, and I'm wondering -

Is it ok running XP with a host file thats large like that ? Would it slow down net access ?
Would something like a 600K hosts file consume that amount and more of memory ?
Is there another address I could assign these to ?, because forcing them to 127.0.0.1 seems to mess up any local servers I might be running

Thkx ..cheyana

Disable your DNS cache if you have a large hosts file. The DNS cache is listed as "DNS client" under services.

Also, I hear that "0.0.0.0" is faster than "127.0.0.1," but it may mess up any proxy services, which I don't suspect you are running.

catch

If you Linksys is recording outbound traffic to 'ads.msn.com' 'feeds.msn.com'......then a computer plugged into the system is connecting to those sites.

Possibly MSN Messenger is running ?

catch .. ok, I will try that idea

dcongram, yes, messenger is running too - so I should'nt block out ads.msn.com and feeds.msn.com if I use msn ?

ty .. cheyana