Most should do, atleast some english is taught in most places in Japan, so most should know the alphabet enough to know what romanji sounds like.

But its not that hard in windows to use the Japanese ime keyboard, just go to control panel, change keyboards or other input methods, change keyboards then click add, and find the Japanese container, then keyboard and choose Microsoft ime.

Then you can use the left alt +shift key to switch between input methods.　こんいちわ。　yep that was written with it, they will not mind if you just use hiragana and katakana too much, they will atleast know what you are talking about.