It opened on 3/19/2008. So I assume Monday, 4/19 or Tuesday, 4/20. But that's only if you were granted IPO shares by the investment houses that offered it. The rest of us can obviously buy and sell at any time, like Angst pointed out.
Regarding your question on valuation, Sunshine, see Hexdek16 's simple analysis above. The IPO opening price was fairly priced compared to Mastercard at 230, i.e. V at $38 with 775M shares outstanding is the same price as Mastercard with 6 times less shares at 230. So to randomly say that Visa goes into the 200 dollar territory because Mastercard did makes no sense. Not to say that it won't go higher for some other momentum reason. Like when China buys it up, etc.
Realistically though it should only go higher from here if it's outlook is better than Mastercard, and that analysis hasn't been made yet from what I've seen (although I didn't see the accounts you read). I sold yesterday above 67 and will see what happens by my settlement day. Whon knows, I might pull the trigger and get back in. But I got my designs on RIMM, FWLT and DE (might dump MON at 122 or 123 to buy DE?).