[2005] caching listbox contents??

ok i a have a combobox (category)...and a listbox(items) when i choose a category..the items for that category is listed in the listbox... the items are take n from a text file.... there are a category which has a lot of items (like 6000).... so it takes some time for listbox to fill up.... for this categorym i want to cache the items to be displayed so that i don't have to fetch the items from textfile each time....

i have tried this
add a second listbox..when i choose the category in question for the first time, i fill up the main listbox with the items and i copy the items to listbox (using list2.items.addrange(list1.items)

so, next time i choose that category, i load it from the second listbox (using list1.items.addrange(list2.items)... instead of reading from the file... the delay is smaller but there's still a delay...

any better caching mechanism ?