Can my internet (IE7) use be tracked at work, even if i delete history, cookies & temp internet files?

I work for quite a liberal company and we are allowed to use the internet for personal use at lunchtime etc. But sometimes when things are quite I can spend half the day surfing. I always delete history, cookies & temporary internet files from outside the lunch hour. But can my illicit surfing be found out by other means?? I have recently upgraded to internet explorer 7 but I don't know if this makes things better or worse... help an internet junkette!