Venture capital firm Andreessen Horowitz is best known for high-profile investments like Zynga, Foursquare and Skype. But the fund, headed by Netscape co-founder Marc Andreessen and his longtime business partner Ben Horowitz, is also betting big on business-to-business upstarts, and these days that means backing companies that enable or rely on cloud computing.

Last summer Andreessen Horowitz made its first cloud computing investment, leading an $11 million round in Okta, a startup that helps companies manage Internet-based applications. Earlier this week, Okta announced its official launch at a press event in San Francisco. Horowitz attended and I later caught up with him to ask about the firm’s strategy for investing in the cloud.

“I look for companies that really anticipate what the new problems are going to be as opposed to solving the old problems for new customers,”  Horowitz said.

In other words, the budding cloud economy has created new challenges for IT departments. And Horowitz is searching for companies that are building solutions specifically for the cloud, not just porting the same services that worked in on-premise, server-based environments.

For example, how do you manage employee accounts for a growing number of cloud-based services like Salesforce.com (CRM), GoToMeeting and Citrix (CTXS)? That’s the new problem Okta is trying to solve. The company helps IT control access to all kinds of Internet-based applications. It also lets employees sign on to multiple services with one password.

Horowitz said investing in Okta was sort of like putting money in drive-through restaurants or roads when the automobile first came out.

“It turned out most of the economic growth came from things that were products of automobiles,” he said.  He sees the same thing happening with the cloud.

Okta may have been the first cloud investment for Andreessen Horowitz, but it wasn’t the last. In less than two years the firm has raised almost $1 billion, and it’s used its impressive reserves to invest in a handful of other small cloud computing players, including PiCloud, SnapLogic and Proferi.

Horowitz says he’s met with over 100 cloud startups to date. While Andreessen is the better-known half of Andreessen Horowitz (not only did he invent the web browser, he also sits on the boards of Facebook, Hewlett-Packard and eBay), Horowitz is your man if you’re a cloud startup looking for some cash.

But don’t go pitching to him if a professional sales team isn’t in your business plan.

“I get tired of people telling me they don’t need a salesforce,” Horowitz said. “A lot of companies want to bypass the CIO. But the customers haven’t changed. The way they buy is via salespeople, and you still need a good old-fashioned salesforce.”

Of course, there are plenty of other VC doors for cloud startups to knock on. Andreessen Horowitz isn’t the only firm pouring millions of dollars into the cloud. Last year we saw several high-profile cloud deals, like Hewlett-Packard’s (HPQ) $2.35 billion acquisition of 3PAR. Plenty of Silicon Valley venture capitalists are hoping for similar exits.

But Horowitz, who has called himself “somewhat of a domain expert in all things cloud” cautions that while Internet-based computing is paving the way for new opportunities in the enterprise, most IT shops are still oriented around the old way of buying and deploying software.

“Everyone realizes that it [cloud-based applications] is a better and cheaper model,” says Horowitz. “But it’s going more slowly in the enterprise than anyone had predicted.”

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