Back again.
Actually it would be "sen en" not "sen yen". There is no "ye" in Japanese. I don't know how it happened that we got "yen" out of "en".
Let me explain what I meant by "Chi = ? ... 1000 = ?". Actually these question marks were meant to be the characters but, as I'd expected, they didn't come out right.
Of course, it is no coincidence that katakana "chi" looks like the Chinese character for "1000": this is what it is derived from. "Chi" is the native Japanese pronunciation of the character (kun-yomi) but the Sino-Japanese pronunciation (on-yomi) "sen" is more commonly heard.
I'd be surprised if Chihiro in that movie had written her name in katakana: names are usually written in Chinese characters. I think I know the movie Xatufan is writing about: it was on TV a while ago but I only saw bits of it.
Is it the one in which the witch has an enormous head and flies like a bird, the one in which the witch has a huge baby that turns into three bouncing heads, the one in which the girl's parents have turned into pigs or at least so she thinks?
I saw that scene in which the witch absorbs most of the girl's name. I thought the character was "1000" not "chi" but I really don't remember: I wasn't paying a lot of attention.
In Steve K's experience ...
"You need the Romaji for the first few months or there is just too much strange stuff happening at once."
This is not my experience but everyone is different. The first thing I really concentrated on was hiragana. I made an effort to write any new word I learnt in this script. I believe that, in the long run, I have very much benefitted from this.
If there is "just too much strange stuff happening at once", my advice would be to leave that other strange stuff alone for those few months and learn hiragana first. Of course, though, everyone is different and this may not be for you.
If you want to use Roman letters ("Romaji" in Japanese), I'd suggest not relying on it for months but only a few weeks. Also, make an effort to use the hiragana alongside side of it whenever you have the time, i.e. write the word in hiragana with the romanisation above it.
Another thing to be careful of is what system of romanisation you're using. There are three which are well known: Nihon-shiki, Kunrei-shiki and Hepburn. Read about them here
http://en.wikipedia.org/wiki/Romaji Often you'll find mixed or confused versions out in the real world.
Hepburn is the most commonly used and has the advantage (for English speakers) of following English spelling (at least for consonants but be careful of "a" and "u", also be careful of "o" if you're from North America). Nihon-shiki has the advantage of having a one-to-one correspondance to and from kana. I don't know of any advantage that Kunrei-shiki has: it more or less combines the worst of both systems.
If you want to romanise Japanese words, first choose a system. You could invent your own system but you might have to explain it if you want it to be read by others. I'd advise against mixing systems willy-nilly (as many people seem to do) but there'd be some sense in mixing them in a systematic way (to get the best of both worlds ... as opposed to Kunrei-shiki's worst of them).
Also be careful of these particles:
1A) "ha" verses 1B) "wa"
2A) "he" verses 2B) "e"
3A) "wo" verses 3B) "o"
A) "Kare ha happoshu wo koen he mote kita." verses
B) "Kare wa happoshu o koen e mote kita." i.e.
C) "He brought a cheap beer-substitute to the park."
The (A)s correspond to how the sentence/particles would be written in hiragana but the (B)s are how it/they would be pronounced. (C) gives the English translation. What do you use (A) or (B)? I'd go for (A).
Steve K also says "Ignore katakana or at least do not put too much effort into it." I disagree. If you plan to live in Japan or just to visit and you know English, then you'll find katakana to be of great use. Company names, product lables and menus are often written in katakana. Often this katakana is a transliteration of English (especially in the case of product lables and bar and restaurant menus).
Once (s)he can read katakana things become ever so much clearer to the English speaker. If you only want to learn Japanese then, sure, leave katakana till later but if you actually want to survive Japan, get onto it as soon as possible. And, let's face it, the main reason anyone would want to learn Japanese would be to get by in Japan.