If all you are wanting to improve your computer for is to download, manipulate and save pics:
Why not purchase a copy of W98se.
I know it is obsolete, but for what you are wanting it is the cheapest bet, and it would give you USB.
Put another 256mb of memory, if your board will take it.
Buy a card reader, a CD-RW drive, and a program like PSP.
You do not need a top end computer for photos, I used an old 266mhz PII with 384 ram for years and it did the job admirably.