Knowing that there's a small war between Thai and Cambodia at Preah Vihear. Is it safe to travel at this time?
Cliff, Siam Reap is fine, but under no circumstances go to the temple on the border.... always take care when travelling near the entire border with Cambodia (it is the Golden Tringle after all and you might bump into some drug runners who'd rather no-one knows they're there.).
here's a news article to help you understand what's going on:
and here's a little map I made for you to ease your concerns.
http://maps.google.com.au/maps/ms?hl=en&ie=UTF8&msa=0&ll=13.984711,104.004822&spn=1.76428,2.782288&z=9&msid=209802967444240303743.00049bce8880f946e2d53 almost 10 years ago
Phil has painted it accurately, the journey between SiemReap and the temple location is over 7 hours by car - it is a LONG way! If you want to head north into Thailand you can go over at the border crossing nearest Prasat at O'Smach. Or head toward Laos and go over there (you can come back out of Laos at multiple places along the journey north.
At Siem Reap make sure you go out at daybreak to avoid the real rush - although this now so well known that there is a rush at daybreak, but the light, the buildings in that light, are very very amazing. Enjoy. almost 10 years ago