Do you actually need to process the text file? If not, then you can probably skip most of the content pipeline.
Something like...
string filename = "Content/TextFiles/sometext.txt";
string path = Path.Combine(StorageContainer.TitleLocation, filename);
string lineOfText;
StreamReader sr = new StreamReader(path);
while ((lineOfText = sr.ReadLine()) != null)
{
// do something
}
Also, be sure to set the "Build Action" to "None" and the "Copy to Output Directory" to "Copy if newer" on the text files you've added. This tells the content pipeline not to compile the text file but rather copy it to the output directory for use as is.
I got this (more or less) from the RacingGame sample provided by Microsoft. It foregoes much of the content pipeline and simply loads and processes text files (XML) for much of its level data.