thanks,

i am fully aware that i need to fully reinstall my system if i do this. i need to anyway as i am upgrading windows to thw 64bit operating system. just wondering if i should kill 2 birds with the one stone

You should probably not do that. The computer will know you have a new drive, but it will be a blank drive that needs formatting and windows installed, as well as all your programs and files so make sure you have all your installation disks--windows and programs and drivers--and all your personal backups. If you are having problems with the drive you have now, contact Dell for a free replacement. Maybe buying an external hard drive would be better to free up space on the drive you have now. Also be sure that your operating system and bios support a 500gb drive. Hard drives are not memory--just space for your operating system and files.

You can purchase Windows 7-64, yes.

i already have windows 7 64bit, is it ok to change my harddrive while i am installing the new opperating system

Of course, yes.

By now your software support will have expired anyway - were you to have to return the system for service, just put the old hard drive back in.  The hard drive is customer-replaceable and upgrading it will not void the hardware warranty.

is it ok to do this even though i am still under warranty? if i had issues would dell be abel to tell i swaped the harddrives?

You should probably not do that. The computer will know you have a new drive, but it will be a blank drive that needs formatting and windows installed, as well as all your programs and files so make sure you have all your installation disks--windows and programs and drivers--and all your personal backups. If you are having problems with the drive you have now, contact Dell for a free replacement. Maybe buying an external hard drive would be better to free up space on the drive you have now. Also be sure that your operating system and bios support a 500gb drive. Hard drives are not memory--just space for your operating system and files.