D2-XL supports D1 levels, meaning, you can play your favorite D1 maps.
Oh BTW:
Welcome to HLP. Please keep all appendages within the installation at all times. Flamethrowers are located underneath all seats, however, due to the rising cost of oil, the ID / evolution debate (don't debate me on whether or not there is a debate),

, and the meaning of life, the napalm has been replaced with Holy Water. Plasma rifles are located in the weapons locker, but only Admins,

, or a hyper-intelligent shade of blue have access to these areas. If you meet a Shivan in the ductwork it is most likely Carl, give him your lunch and back away slowly, odds are good you'll be fine. Recommend reading includes
Karajorma's Freespace FAQ for general questions, and
The Freespace Wiki for specific issues and questions.
Also, watch out, Holy Water can burn, and the flamethrowers are usually out in the main HLP forum