How can I connect my two pcs with a serial cable without using a router and which type of serial cable do I use? Can I use an ethernet cable?

Ethernet and serial cables are different cables. Using a cross-over Ethernet cable, you can connect two PCs with network adapters directly to each other - no switch or router needed. With a serial RS-232 null modem cable, you can use the Direct Cable Connection feature in later versions of Windows to connect two machines. The Ethernet option is the way to go for speed and simplicity, even if you need to buy network adapters. Then again, if you have to buy adapters, you could get wireless adapters and connect them in ad hoc mode.

We used to use the serial connection with MS-DOS 6.22 when Windows 3.1 was the current flavor du joir. It was sooooooo sloooowwwwww. Go with the Ethernet cross-over cable. It is relatively easy and 1,000's of times faster.

In many cases you don't need a crossover cable anymore. Many NIC's can auto sense and you can either go through a router, or direct. But, just to be safe, I'd go crossover. It'll work for sure then, but sometimes there are regular ethernet cables lying around. If so, give it a try.

Don't have to use serial cable anymore.. If both of your computers are equipped with network adapter, then just use a crossover cable to connect both computers to share files, etc..