Degrading Performance

Hi, I am running Vista Home Basic on an ACER PC with 1Gb Ram.

The performance of the PC degrades dramatically when the system is in idle -
ie I leave the PC on when I go out, or over night (Powers settings to always
on). I have to reboot the system on a daily basis, otherwise the HD "churns"
and it takes MINUTES to open an App, or even swap between open Apps.

XP - No such issues

My Main apps are IE7, Adobe CS3 and Outlook 2007
Used RAM usually sits at 58% - 65%
HD 70% free on 160Gb

Please help, it took me 8 minutes today to log in, after leaving it on all
night, copy a 144Kb file from a removeable HD to E-mail and sent it.....