If you are using current VAIO series, theres is one option to limit/stop the charge when it reach at certain percentage of your choice. You must insert the battery in order to enable this feature.
Click at VAIO Control Center, and navigate to Power Management. Then click at Battery Care. From there you can customize at what range the power will stop charging the battery.
Google works wonder.
http://esupport.sony.com/US/perl/swu-list.pl?mdl=VGNNR240E

usually you might lose some feature in Vista when dowgrading to XP.

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Added on August 8, 2009, 12:37 am

both VAIO NW and Acer Timeline are different category.
im not experience this model, but if you look at the spec sheet for VAIO NW and Acer Timeline, the NW wins on processor than Timeline, tho Timeline beats NW in battery life. Please refer to resolution. high resolution LCD will decrease the battery life (e.g: 13" stay longer on batter than 15").

if to stay connected with battery for long hours is your purpose, absolutly Acer Timeline as the choice.

where can i check the temperature?