i didn't tell my employer at the time, and i got the job while applying for med school (the fall of my application season) ... they asked me what my future plans were when i interviewed, and i told them at some point i saw myself going back to school, but that i didn't know when that would be. (the truth - who knew whether or not i would get in, after all.) this was a mid-sized company, so i was a little more than just a cog in the machine, but not too much more. i wasn't drop-of-a-hat-expendable, (the position required prior experience or pretty comprehensive training) but i could be replaced in about a month's time, if necessary.
when i took time off to interview, i just told them it was "personal time," and i only used days allowed by the company - i.e. i didn't take any extra time that wasn't afforded the rest of the company's employees. nobody asked, as it really wasn't their business. personal time is just that - personal time.
when i left the job about 8 months later, i just told them i had an opportunity elsewhere that i couldn't turn down. everyone wished me the best, and nobody pried.
telling them i was applying for that application cycle would have likely led to my being let go, depending on who it was that i told. i needed the income and didn't feel i was being dishonest. i gave 3 weeks notice, and left about a month and a half after i made my final decision about where i was going to go to school. it all worked out well for me.
good luck w/your situation.