The answer is yes, it will work. But it's not the best way to do it. If you have all the ports in the same vlan, the switch basically acts as a layer 2 device. As such, it doesn't care about IP addresses, it will track MAC addresses and when PCs want to communicate with each other, they will send out ARP broadcasts trying to find the MAC of the IP its looking for. When this happens, all devices on the switch will receive the broadcast and need to process it. If they do not have the IP address they simply drop the ARP packet. This is inefficient since it all devices will need to process all broadcasts. On a small network this isn't a real issue, but on larger networks this grows exponentially.
As you indicated, you will need a layer 3 device to route between the subnets. Setting up 2 interfaces on a router will work, assuming the ports are on the same router and routing is setup properly. Another option is to use sub-interfaces on a single router port each with an IP address from the 2 subnets.
All that being said, it begs the question, Why? If you are going to allow traffic between the subnets, why have 2 subnets on 1 vlan. If you are limited to a single vlan, why not just use one subnet? There's alot of unnecessary packet traffic on your network. I'm sure you have your reasons, and I hope I've helped clarify a little.
Rob
