Don't feel limited by your machine not being up to the task of mining. I've got the same problem. You can still make small amounts of Bitcoin using pay-per-click sites like
Bitvisitor though. It's not as much as you'd get from a decent mining rig, but you have to pay quite a bit up front to get one of those, not to mention the higher electricity bills, so pay-per-click is probably the more profitable option nowadays. You make smaller amounts, but you don't pay anything up front.