Do you really want what you said, and sort the items, or do you just want to find them using the categories as keywords/tags? If the latter, you might look at
NoteFrog. The current version can import files delimited with markers.
If you really want to keep your text organised, then you might try a single-pane outliner like
Noteliner. It's free, but .NET if that bothers you, and uses its own file format.
Otherwise, I concure with MilesAhead, though I normally reach first for
MemPad. MemPad has particularly nice input/output from/to delimited files. It shouldn't be too hard to massage your files into forms that NoteFrog or MemPad can import.
FWIW, following MilesAhead's comment, I do know that
Ultra Recall Standard or Professional can import Treepad Lite .HJT files. Some of the other outliners, like
RightNote and
AllMyNotes, only accept
KeyNote .KNT files, but KeyNote is free and can import .HJT files itself, so you can convert in two stages.