Windows Vista: Hard drive space getting smaller?

Hard drive space getting smaller?

Hello everyone,

I've have noticed that my hard disk C: was getting smaller every week. From 50.1 Gig it was down to 11 Gig. I deleted unnecessary programs, transferred my music, photos, and other files to my drive D. I also tried disk clean up and deleted restore points. But still, the drive space gets smaller.

Is this really because of windows updates? is it ok to delete old updates?

I reset my computer to its factory default system ( with vista, trial versions of Norton and MS office). But I noticed that my 50.1 Gig in drive C was down to 30.1 Gig. Do these programs really take so much space?
Below is the system info for my pc. Thanks in advance for your help.

OS Name Microsoft® Windows Vista™ Home Premium
Version 6.0.6000 Build 6000
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Name SIRRICHARD-PC
System Manufacturer Acer, inc.
System Model Aspire 4720
System Type X86-based PC
Processor Intel(R) Core(TM)2 Duo CPU T5450 @ 1.66GHz, 1667 Mhz, 2 Core(s), 2 Logical Processor(s)
BIOS Version/Date Acer v1.3709, 8/27/2007
SMBIOS Version 2.4
Windows Directory C:\Windows
System Directory C:\Windows\system32
Boot Device \Device\HarddiskVolume2
Locale Republic of the Philippines
Hardware Abstraction Layer Version = "6.0.6000.16407"
User Name SirRichard-PC\Sir Richard
Time Zone Taipei Standard Time
Total Physical Memory 1,525.81 MB
Available Physical Memory 353.69 MB
Total Virtual Memory 3.21 GB
Available Virtual Memory 1.61 GB
Page File Space 1.78 GB
Page File C:\pagefile.sys