keterys has already mentioned them, but I think it bears repeating that there are rules in the DMG - on pages 187-188 - for creating non-elite NPCs of any standard race and class combination.
So you could use this to create a standard 7th level Dwarven Ranger NPC, who would be worth 300 xp.
NPC vs PC
I highly recommend you use the NPC rules for creating the Ranger, rather than generate him via the standard PC rules. The NPC rules remove a few elements from the character. Some of these, such as feats, are bypassed for simplicity - but others, such as a limited number of powers, are bypassed for balance issues.
A 7th level Ranger PC will have two Daily Powers available - each of these will be significantly more powerful than anything a standard monster of that level will have. Add in several Utility Powers and Encounter Powers, and the enemy has a much higher threat level than is appropriate.
This is because a PC has many powers they are expected to go through over the course of a day, while monsters only have to worry about one encounter - the fight with the PCs. The more powers they have to burn through in that one fight, the more dangerous it will be.
Hence, I highly recommend using the standard NPC creation rules, which will produce a 7th level Ranger that is a perfectly reasonable as an opponent for the PCs.
XP Budget
A standard encounter for that party would have an xp budget of 825 xp (250 xp for each 6th level character, 175 xp for the 4th level character, 150 xp for the 3rd level character.) DMG page 56 has the chart for this, but essentially, each character contributes to the xp budget the value of one standard monster of their level.
Thus, if you do use the standard NPC rules, your Ranger is worth 300 xp. The remaining 525 xp can be spent on dwarves - say, a Dwarf Hammerer (200 xp) and 2 Dwarf Bolters (175 xp x 2 = 350 xp). You come out 25 xp over your budget, but that is still well within the range for a standard encounter.