How good is the ISO on the Nikon D70?

In terms.of shooting in low light conditions. And i have a D3000 and a friend wants to.trade for his d70… Good deal?

Not really. The D3000, although not one of Nikon's best is much newer and advanced than the ageing D70.
The D70 was a bit more semi pro spec with some of its features, such as 1/8000 sec shutter speed / internal focus motor so they are not quite comparable, but the d3000 is definitely a better option.

The D70 has a better body build, but an older, inferior image sensor, it's bottom of the barrel for noise at high ISO, don't bother with it. For the money, if you want better high ISO performance, you want the D3100, (skip the D3200) D5100, D90, D7000.