Is your new girlfriend asking for a one-baht gold ring? Watch out, as this isn't the cheap trinket it sounds like: for jewellers and goldsmiths, the baht is also a measure of weight, or 15.244 grams (around 0.5 oz) to be exact. At 2006 gold prices, one baht of gold would thus cost you well north of 10,000 baht in cash!
The currency of Thailand is the baht (THB, ฿), written in Thai as บาท or บ. There are six coins and six notes:
25 and 50 satang (cent, copper colour) coins - nearly worthless and only readily accepted (and handed out) by supermarkets and 7-11s
1, 2 and 5 (silver colour) and 10 baht (silver/gold) coins
10 (brown - now very rare), 20 (green), 50 (blue), 100 (red), 500 (purple) and 1000 (grey-brown) baht notes
The most useful bills tend to be 20s and 100s, as many small shops and stalls don't carry much change. Taxi drivers also like to pull the "no change" trick; if caught, hop into the nearest convenience store and make a small purchase (or ask them for exchange).
ATMs can be found in all cities and large towns, and international withdrawals are not a problem. When using a debit card, an ATM will typically provide a much better exchange rate than a money exchange counter, and this is especially the case if you have a card that does not charge a transaction fee for overseas withdrawals (becoming common in countries such as Australia). ATMs are available at Bangkok's Suvarnabhumi airport (BKK) after collecting your bag and clearing customs, and while it is advisable to arrive with a small amount of baht if possible, you may want to obtain most of your cash from an ATM after landing.
More remote areas (including smaller islands) don't have banks or ATMs, so cash or traveller's checks are essential. Many hotels and guest houses will change money for guests, but hefty commissions and poor rates may apply. US dollars in small bills (1s, 5s, and 20s) are invaluable for onward travel to neighbouring countries other than Malaysia, but are only useful in Thailand for exceptional purchases (eg paying visa fees for Cambodia).
Credit cards are widely accepted in the tourist industry, restaurant and shopping mall or widely used in Bangkok and major cities.