Hello Jeff,
Unfortunately, ip accounting is not supported on 4000 & 4500 series platforms... I have attached a doc, which gives the software features supported for one of the extended IOS versions of SUP IV... 4500 series have an advance feature called Netflow, which you can use for troubleshooting purpose.. but for that i guess you need to have the netflow daughter card installed on your supervisor engine...
You can also have a look at the datasheet of SUP IV to know more on netflow...
http://cisco.com/en/US/products/hw/switches/ps4324/products_data_sheet0900aecd8035cf2b.html
Hope this helps.. all the best.. rate replies if found useful..
Raj