Slow WiFi router from ISP affecting internal transfer rates?

I have a 802.11 b/g wifi router that was provided by my ISP. The plan I subscribe to gives me about 650kB/s down. Which is fine... I understand you get what you pay for.

To this router, I had two computers connected by wifi. Both computers have 802.11 b/g/n cards. Internal network transfers between the two computers never go faster than about 300kB/s over wifi.

Thinking the router might be the issue, I connected one of the computers to it with a normal cable. I could then get internal network transfers of about 550kB/s. I can't wire the other computer because it's in a different room.

I called my ISP and asked if they'd replace my router with an 802.11n model. They said no because it's not defective.

So my question is: would obtaining an 802.11n router improve my internal transfer rate? If so, I can complain more forcefully, and/or purchase my own, which I would wire to the ISP's router and use to distribute the signal within my house.

Thanks in advance...

If it's a virgin media 'super hub' replace it as soon as possible, they have the worst wifi of any router I've ever seen. Cuts out randomly and you're lucky if you hit 500k on a 50mb connection.

Sounds rather similar.