SWhen Wall Street fails, Silicon Valley must step up. So goes the hubristic thinking here. Debt greases the wheels of commerce, and the sale of servers and software is no exception. And that part of the credit industry has hit a rough patch, too, with defaults on equipment loans nearly doubling in the past year. As with other credit markets, this had made traditional lenders nervous. So cash-rich tech companies are venturing into lending themselves. IBM has long had an in-house lending arm, with $24.5 billion in loans outstanding. Cisco lent $4 billion to customers last year. Even eBay is getting into the game through Bill Me Later; it acquired $550 million in consumer loans in conjunction with the purchase of the payments startup.We know how this ends — with tech-company shareholders footing the bill. Cisco wrote off $900 million in bad debt in 2001. It will surely claim to have learned its lessons since then. But as others rush in to help customers acquire their wares, some will surely get burnt. As will investors, who may think they're buying shares in a tech company, only to discover they've put money into a bank.