The Digispark has a fairly limited amount of memory and can drive roughly one hundred pixels at a time. If you need more you can network several digisparks together or you might be able to reinitialize the NeoPixel library on a different digital pin and use the same section of memory to write out to another strand, with potentially six different strands of 100 or so LEDs each.
To use the NeoPixel library make sure to download the latest version of the Digispark Arduino software (currently unreleased - check back later) which includes the DigisparkTinyPinChange library. Choose the 16.0mhz NO USB board varient. 800khz NeoPixels and WS2811 LED strands are also compatible with the regular 16.5mhz (Tiny Core) board option. 400khz (NeoPixel v1) haven't yet been made compatible with 16.5mhz clock speeds.
The included example sketch works great with Digisparks - just change the output pin from 6 to a lower number and plug your pixels in. It's safe to connect your pixels to D3 and D4, but you'll see some crazy colourful glitches during program upload and before your sketch starts when powering your digispark from a computer.