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It should be the same engine so it should have the same (similar, i mean) files. Wouldn't it be possible just to extract the contents of episode II and IV and replace them over the Dreamcast's episode I? Then the title could be changed so there would be the epiosde under the title.

Im just drawing squiggly lines in the air, but it could work. Yes? No?

Would pretty much require ep1 beeing replaced with ep2, with each area loading a different area of ep2 (forest would load seaside for example), however, since ep2 is either in gc files and blue burst files, you would need to convert everything to a format the dreamcast can read, i believe that's not possible and even if it is i doubt it would work.
Replacing an area might be possible, but a map with enemies or a full episode would be just impossible.

EP4 demands more resources, the dreamcast would not be able to handle it.

Best you can do is play PSO BB with a controler because i'm sure ep2 and ep4 on the dreamcast will never happen.

As stated by K_I_R_E_E_K, even if you got the files converted there's still the matter of system resources. Episode IV clearly wouldn't be possible on that count. The level designer for Episode IV went absolutely bonkers creating insanely huge maps with ball field size open areas, made possible by the user determined nigh limitless resources of a PC.

Episode II is a bit muttled as we know it was originally being developed for the DC, but was then bumped off for re-engineering to conform to Game Cube system development. Purely my own speculation but, I think the level designs for Episode II were redeone after the DC version development was scrapped because the GC had the system resources to support much larger level maps. So here again, even if someone could somehow convert all the files into something the DC could interpret there is a good possibility that the actual area playing fields could require a greater amount of memory to handle than the DC has available.

Much as we would all like to believe that the possibilities our beloved DC can do are boundless there are limitations to everything.