If you bought SD card w/ OS installed inside, maybe you don't have to use cable or monitor. Just connect Pi to your router via ethernet cable, then find what ip address assigned to Pi, then connect via SSH.
But if you want to use GUI desktop, you have 2 ways.
i) Get a cable/converter/screen
ii) Install x11vnc on Pi through SSH which explained above, then run x11vnc server on Pi. After running x11vnc service, you can get Pi's GUI screen through a VNC connection.
1b) Raspberry Pi has 2 different way to connect to screen/monitor/TV. HDMI and RCA, so if you have RCA cable and your screen/monitor/TV has RCA connector (http://en.wikipedia.org/wiki/RCA_connector) you can use it to connect. I have a setup with RCA cable to connect my old CRT TV.
What you need;
* Raspberry Pi (Model B)
* SD card (installed OS of course)
* USB Keyboard
* USB Mouse
* RCA or HDMI cable to connect to screen/monitor/TV
* Power supply (5v/1A)
* Wi-fi adapter (choose known verified vendor/model : http://elinux.org/RPi_USB_Wi-Fi_Adapters)
* External powered USB Hub (in case you want connect more USB devices)
Of course you can use converters like DVI->HDMI. But think that, HDMI is digital, RCA is analog.
I'm using a DVI-HDMI cable because my old LCD monitor uses DVI connection, but at work I'm using a HDMI->Display Port converter to connect my HP monitor with Display Port. Converters mostly works.