Heh, you might still want to consider that new PSU...I'm not sure anyone's ever even heard of the brand of PSU you have. Where did you get it? If it came with a case there's a good chance it's very low quality. It sounds like you're splitting wires...once you start doing that it's likely that you're running low on amperage. Key note - too much power is bad for your hardware, but too little can be even worse. That said, your system might SEEM fine, but if you start to really tax it, it could crash. Most people will tell you not to skimp on your PSU. A good steady supply of power is a MUST. You might be alright too. You could try the online PSU calculators to figure out how much power you really need, and also check the amps you're using. As a general rule, if you want to avoid mishaps, do LOTS of homework.
Another note, since you might not be from the UK...check out Thermaltakes add-on PSU.
www.thermaltake.com You can find out more about it there (not a direct link to the product)
You may want to just consider getting that, it could always come in handy in future builds too and it costs a good deal less than a whole new PSU.