Specialty Grains, To boil or not to boil

For a partial mash (malt extract plus specialty grains), do not boil the grains. Put them in a large mesh/muslin bag and steep them in your brewpot at 155f for 30-45 minutes before adding your hops or extract.

Boiling the grains would release harsh tannic flavors that you don't want.

To expand from Chris Dargis's comments, specialty grains are called that because they contribute more flavor than they do fermentable sugars. In extract and partial mash brewing (what you're looking at doing), the fermentable sugars come mostly from your extract, where the specialty grains supplement the beer by contributing other characteristics such as flavor (e.g. sweet, caramel, honey, biscuit, roast, depends on what type of grain), mouthfeel and head retention. Opposite of using extract is brewing using the all-grain brewing technique, where the brewer uses "base grains" instead of extract to get his fermentable sugars, as well as specialty malts. Similar to partial mashing, all-grain brewing requires the brewer to soak the base grains and the specialty grains together before filtering out the grains and boiling the wort. In reality, partial mash isn't the best, most intuitive title for the technique, think of it like a mini-mash.

As Denny explained, you do not want to boil specialty grains when partial-mash brewing. Water has a fairly high pH to start out with, which influences the extraction of tannins from the grains at high temperature, resulting in an astringent/bitter flavor (different from hop bitterness). Tannin flavor is never desirable in beer. The reason decoction mashing (part of all-grain brewing) can boil grains without extracting tannins is because the wort that they are boiling has a much lower pH than what you'll have when partial mashing. The reason it is lower is because they are soaking both their specialty grains along with their base grains, which when mashing both together, the pH is much lower than if you only steeped your specialty grains alone. You'll want to maintain a steady temperature between 150°-160°F for the steeping grains (assuming they're all malted grains being used). Any higher, and you'll extract tannins, any less, and you won't get the optimal sugar extraction from the grains. I've also seen some really wonky looking beers where they boiled the grains and the entire carboy looks like one giant yeast/protein cake.

As a bit of an aside from your two questions, here's an interesting, informative video from Brewing TV where they brewed two batches of beer of the same style. One was brewed partial-mash, the other all-grain. It helps to clarify the differences, and show how they compare in the end with tasting notes.

Specialty grains need to be soaked in water at an optimal temperature for alpha amylase activity - 150-160F. Typically, 30 minutes is enough time for full flavor and sugar extraction. However, with specialty grains only, you aren't looking to get many fermentable sugars from the grains - only wort color and flavor. If you steep them in water hotter than 160F, you won't get many fermentable sugars extracted from them.

I would recommend just steeping at the temperature mentioned above. You do need to avoid burning the grains with direct heat contact. Also, avoid squeezing or compressing them as this will extract unpleasant tannins.

Edit: Removed statement that boiling grains is not dangerous in a partial mash.