I vaguely remember an anecdote from my British History class, that before her arrival in England Katherine of Aragon and Arthur, Prince of Wales wrote to each other in Latin, only discovering after their first meeting that since they'd learnt different pronunciations they couldn't understand each other.
Hence my figuring written forms remain much more static and resistant to change than speech.
Yes they could. Clerical and proto-clerical script began to develop around that time, and clerical script characters are fairly intelligible to modern Chinese readers (more so the ones accustomed to "traditional script" vs. "simplified"). Here's an example of the various scripts over time in Chinese writing: http://www.ngansiumui.com/about/ebook-callig_ch02_5-scripts_600x340.jpg .
The style of writing was different though and there would be major difficulties in translation for an untrained modern reader. There have been major reforms in the 20th century on the Chinese written language to make it more accessible to the masses, increase literacy, and bring it closer to spoken language. Written chinese of that period obviously lacked those reforms. That said, Han-era (100 BCE being right around the middle of that era) texts are taught in high school in China.
