Space Manager in HDCleaner

I looked at the space manager for my drive in the HD Cleaner and it came up with some things in bold and I was wondering about that.
First let me explain that I have 2 computers this one that I am enquiring about has an OS of WinXP Pro the space manager came up with this..
Main Drive Total (C Drive) 5294.30 MB
Program Files 760.00 MB
Common Files 184.62 MB
Microsoft Shared 31.18 MB
Symantec Shared 117.98 MB
Windows 2101.05 MB
$NtServicePackUninstall 313.84 MB
Service Pack Files 501.15 MB
System32 623.52MB
There are other smaller files/programs but the ones above have the MB that was in bold. I was just wondering if I need to delete anything as it is taking up too much space???
I just hooked this 2nd computer back up to the net a couple days ago and its really sluggish especially on startup and shutdown. I did do the "Read Me First" tutitorial to rule out spyware and ran my HJT and checked that on a site where you can copy and paste it to check your HJT logs (I can't remember the site at the moment).
So any help on getting this 2nd Computer running better and faster would be appreciated.
It is an HP 512MB of Ram it used to be a WinME but I upgraded it to XP Pro with an Installation disc.
Thanks for any help anyone can give me and if you need more information just ask..

**Ok the tree did not work on here the Program Files is listed under the C drive then common files within Program Files and the 2 shared files within the Common Files.. Windows is listed under the C Drive and then the Service Packs and System is listed under the Windows files..
I just didn't want anyone to be confused even thought you all are very smart with this kind of stuff.. thanks..

 

Thanks for the reply..
Currently I do have enough space I am not close to running out but also didn't know if those figures were too high so that is why I posted to make sure that things were normal.
Currently my HD is 27.9GB and I am only using 5.26GB of that 27.9GB but once I get all my kids' games loaded back on I dont' know what the GB will be.
When I do go to look for a new HD what should I get as far as Brand and size?
This computer is an HP Pavilion 7920 and it is used at home for internet access, and gaming (on line (not downloaded), CD, & downloaded from online).
Thanks..