Multiplayer always takes more resources to run, that's perfectly normal for every game. There are several things you can do to make MC (and other programs run faster)
- don't install texture packs or mods
- set render to Fast (and not Fancy) in the Options menu
- press Win+R, type msconfig, hit enter then click on the Startup tab and untick applications that don't need to run in the background
(just make sure you don't untick programs your laptop needs - though they usually come pre-install with all kinds of crap)
- turn off your firewall and antivirus before playing multiplayer
- uninstall AVG if you happen to use it
- try installing the
Optimine mod that's supposed to make run MC faster (doesn't work for every setup)
- don't use wireless connection to play the game (wired is always more stable and usually faster)
- install WinXP instead of Vista or Win7 (only if you can find drivers for your laptop)
bonus: laptops aren't meant for gaming :icon_razz:
Let me know if you need any help with this. Good luck!