I have old System files on D drive(C is current sys drive), Can i delete them??

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I currently own a HP laptop which i bot in jan 2008. It came with only one drive and single partition in it thats Local (C:). Couple of month ago, my Vista got corrupted. So i gave it to an System admin to reinstall Vista. But the problem was since the laptop came with one single drive partition, both the system drive and my important files wer in same C: drive. So i asked the Admin to transfer those all files from C: (which included some system files too) to his personal Ext hard disc as all my personal files wer mixed up in C including some in desktop. I too wanted him to format the drive, Split the drive partition into two that C: and D: and Reinstall Vista in C: and Reload my old files from Ext Hard disc to (D:). He did the exact thing as told. I wanted to do this coz in future if my systems corrupts again. C drive will be reinstalled but my D drive will be safe and untouched.. Now my system is working fine. But the thing is, I got all my necessary personal files but those Old system files are too there in D drive which occupies almost 3GB of size. My Question is, are these file unwanted now? And do these files dont belong to the current C drive? If i delete these files to free up space, Will it cause any problem to my current healthy C drive?? Simply, Is it safe to go ahead and delete these 3GB old system files???