Svchost.exe High Memory Usage

The pc runs on Vista 32-bit with 1 GB of RAM. PC runs very slow on start up and remains as such for a good half hour. I have noticed in the task manager that an svchost.exe process often peaks at about 600mb. I assume this is to do with Windows update, but it seems to take an eternity before it settles down. I have been through the process of clearing malware etc and have been given a clean bill of health from the malware forum.
Is there anything I can do regarding this svchost using up the memory?

 

PC at this moment is running ok (ish) with no significant memory usage by svchost. As soon as it replicates, I will post the listing.
Thanks in advance.

 

Booted PC today and svchost got to about 450mb when I took the attached screenshot. I've also noticed that the last few times on re-boot, Microsoft Security Essentials is disabled and I have to start the service again

 

Looking at that, probably Windows Update, which has triggered similar problems for many others recently. Setting WU to check but not download might help, disabling it until you need to update would be better but if you use MSE, that would also block updates for that.

Can you start MSE and use it to download updates successfully?

 

MSE is fine - took a matter of minutes to download and install virus definitions update.

Disabled automatic windows update and rebooted. This stopped the PC being unresponsive for hours on end on start up. When I then asked it to check for updates it took over an hour to tell me that there was 1 update to install.

 

Yes, waiting times of an hour or longer have been commonplace recently with WU.