I'm running Windows Server 2003 sp2 on a Dell Inspiron e1705. There has never been a problem going to standby/sleep mode (by closing the laptop lid, or from the Start menu), and then resuming later.
Today I did a Windows Update to install the latest patches and fixes. I don't know if there is a correlation, but now when I resume from standby/sleep mode, the machine does a cold boot.
The AC adapter is connected. The battery is 2 months old, and all its LEDs light up when pressing its test button. The Power Management shows it at "99% (charging)" all the time.
There is nothing suspicious in any of the event logs.