A light twin pilot attempting to get his NEXRAD on line; and feeling rushed by other pilots taxied across the active runway. He wrote his taxi clearance on a page with numbers that allowed him to confuse Runway 13 with Runway 18

Narrative

I was leaving DBQ for a VFR flight. I had checked radar at home and felt a heading on course would provide a safe route through weather. After fueling I was urged by other pilots to move so there was urgency to get underway. Ground Control advised that I needed to check weather on my route due to thunderstorms. I wrote down the active runway on a sheet that contained previous data. My onboard Nexrad radar was not coming on line as I taxied towards the active while I was also talking to Ground Control. A main focus was to get my onboard radar working. While taxiing I looked at my clipboard and read the active runway. I saw Runway 13 when the active was Runway 18; so I taxied across Runway 18 towards Runway 13. The Ground Controller asked if I was clear of Runway 18 and I said yes so he directed me to turn around and hold on Runway 18. After 10 more minutes or so my radar became active and I departed Runway 18. There was no other traffic for Runway 18. To correct the situation I will not get rushed to preflight again and will taxi first and do other things after completing taxi to active; and to confirm the active runway.