if you want to stick to your deprecated and extremely unsafe windows XP then your option is a web wallet like blockchain.info so that at least you are controlling your private keys.
but if you value your security then i suggest trying Linux. there are a lot of distributions that are light weight and even if your computer is old and not-strong you can run them much faster than you run Win XP. my suggestion is Lubuntu, it is Ubuntu with a light weight desktop environment
https://lubuntu.net/ and it looks like windows a little.
you can install it then install Electrum and move your funds from Multibit to the latest version of Electrum.
read the sticky topic for migration tips:
https://bitcointalk.org/index.php?topic=2293714.0