Help Memory card space reduced

[jrdba]

So i had copied several .avi files to my evo's 8gb SD card from my macbook and further on copied them onto a windows xp machine later on. then on that windows machine, i decided to erase all the .avi files which amounted to about 7gigs. now when i connect my evo back to my macbook and check the size available on the sd card, all i see is 766mb available, used 7.17gb on disk and 7.94gb capacity. The format oddly states MS-DOS (FAT32). Looking at the contents, the .avi files are no longer present but it looks like their ghost copies somehow are still there. Should i just format the sd card? any other resolution? thanks folks. My evo by the way is rooted.