Like poopants, I actually was at a jewelry store with my wife and she specified the one she wanted but unlike him, I was going to get that one anyway. I wanted to make sure she liked it since she'll be wearing it the rest of her life. I told her I was thinking about proposing but wondered if she had a preference in rings (obviously she had been pestering me to propose for some time, that's what happens after a while - subtle hints turn into not so subtle demands as I'm sure you've experienced). After I bought it, it really bugged the shit out of her knowing that that I had it and hadn't yet proposed to her....
You might want to think about something along the lines of one of these, this style is becoming very popular. Also, I don't know about your finances, but the amount your spending on that ring you linked seems on the low side.
http://www.tiffany.com/Engagement/Item.aspx?GroupSKU=GRP10015#f+0/0/0/0/0/0
http://www.tiffany.com/engagement/Item.aspx?GroupSKU=GRP10060#f+0/0/0/0/0/0
http://www.heartsonfire.com/shop-je...rings/transcendsinglehalosolitaireforhof.aspx
http://www1.macys.com/shop/product/...772875-_-kw-&gclid=CLKT_5q3wrICFYVQOgod-isARg
You don't necessarily have to go through these companies online. You should be able to find a similar style locally. Also, if you get a ring with diamond chips surrounding it, it makes the diamond look larger.
edit:
I should mention, the ring you linked is 10K gold, that's the lowest quality. If you can swing high quality (18 or 24K) then you might as well go with that or even better if she's willing to go with a silver color, switch to platinum. Platinum is much rarer than gold but oddly enough, the value of gold has gone through the roof from $800 an ounce in maybe 2006 to nearly 1800 an ounce now while the price of platinum has moved up slower. Gold is now a little more expensive than platinum. Given those options, I'd go platinum since it's rarer and IMO it's irrational for it to be cheaper than gold. Eventually (if the world ever returns to sanity), your rings would be worth more if they're platinum than as gold.
FYI: I thought something seemed off about the ring you linked. I asked my wife about it and she told me that the ring with three stones in a row is normally an anniversary ring.
http://www.helzberg.com/category/engagement+%26+wedding/three-stone+rings.do
From the site linked above:
"Celebrate your love with three-stone rings from Helzberg Diamonds. The perfect way to honor your special relationship,
our stunning diamond anniversary rings are expertly handcrafted to last a lifetime. From timeless to modern three-stone diamond rings, you’re sure to find the right ring to symbolize your eternal bond. Serving happy couples since 1915, turn to Helzberg’s three-stone anniversary rings when you want to give her the absolute best."
Since you're looking at Zales, here's a link to Zales' engagement rings:
http://engagementring.theprestigediamondcollection.com/NewEngagementRing/ERing.aspx
When I showed my wife the ring you picked out, she told me that you should take a woman that's already married, a sister (yours or her's), her mother, or someone like that with you to help you find a ring. If you've already asked her father to marry her (assuming you're going the traditional route) then ask her mom to go with you to find a ring for her. Assuming they talk a lot to one another then she should have a good idea about it. Plus you can ask your future mother-in-law her ring size and if she doesn't know it, she can "let it slip" to your girlfriend that you're going to propose and when you go shopping with her, she will just so happen to know her ring size (or you could take your girlfriend ring shopping with you like poopants in the post above and I did). When she knows the ring size, you'll know that she's told your girlfriend but that's okay IMO, it's pretty common and will get her excited that every time you go out MIGHT be the night.
Those engagement rings from Zales' don't include the stone in the price.
Congratulations and good luck! Come back and update us later I'm curious how the ring shopping worked out now.