I would strongly suggest you go to the microsoft updates site and download IE6. It comes with OE6 which fixed a load of loopholes that allow all kinds of scripts to run. OE5 is an open book for hackers.
If you can't update, try opening and closing Oe a couple of times without looking at or doing anything - worked for me.
The only other thing that could be slowing it down is, have you enable some sort of Email protection on your anti-virus or firewall?